Release transport references in Dispose regardless of _shouldDispose

[Copilot]

Fixes: #1971
Device bindings placed the field = null/= null! assignment inside the if (_shouldDispose) guard in Dispose. When the transport is caller-owned (_shouldDispose == false), the binding never cleared its reference, keeping the object rooted longer than necessary.

// before
if (_shouldDispose)
{
    _i2cDevice?.Dispose();
    _i2cDevice = null!;   // skipped when caller owns the transport
}

// after
if (_shouldDispose)
{
    _i2cDevice?.Dispose();
}

_i2cDevice = null!;

Changes

• Moved null assignments outside the _shouldDispose guard across 40 device bindings — the Dispose() call stays guarded (caller-owned transports are not disposed), but the reference is always cleared.
• else-branch cases (GpioButton, Ccs811, Dhtxx, KeyMatrix, Pcd8544) — the branch closes pins on caller-owned controllers, so the null assignment is placed after the whole if/else block, past the last use of the field.

Notes

• Scoped to the null-assignment bug. The autoDispose → shouldDispose rename raised in the discussion is already complete in the codebase; the broader "missing null assignment" cases and the analyzer idea (Code-gen shouldDispose ctor and Dispose pattern #1971) are left as follow-ups.

[Copilot]

Pull request overview

This PR updates multiple .NET IoT device bindings to always release (set to null/null!) transport/controller fields during Dispose, even when the transport is caller-owned (_shouldDispose == false), reducing unnecessary object rooting and improving GC behavior.

Changes:

• Moved transport/controller field null-assignment outside the _shouldDispose guard across many bindings.
• Adjusted if/else-dispose patterns (close pins when caller-owned) so null-assignment happens after the last field use.
• Standardized the pattern across I2C/SPI/GPIO/serial-based bindings and a few shared helper types.

Reviewed changes

Copilot reviewed 40 out of 40 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/devices/Vl53L0X/Vl53L0X.cs	Always clears _i2cDevice reference after guarded disposal.
src/devices/Uln2003/Uln2003.cs	Always clears _controller reference after guarded disposal.
src/devices/Tcs3472x/Tcs3472x.cs	Always clears _i2cDevice reference after guarded disposal.
src/devices/Tca955x/Tca955x.cs	Clears _controller reference outside _shouldDispose guard (but Dispose(bool) needs a fix; see PR comment).
src/devices/Ssd1351/Ssd1351.cs	Clears _gpioDevice reference outside _shouldDispose guard.
src/devices/SoftwareSpi/SoftwareSpi.cs	Clears _gpioController reference outside _shouldDispose guard.
src/devices/SoftPwm/SoftwarePwmChannel.cs	Clears _controller reference outside _shouldDispose guard.
src/devices/ShiftRegister/ShiftRegister.cs	Clears _controller reference outside _shouldDispose guard.
src/devices/PiJuice/PiJuice.cs	Always clears _i2cDevice reference after guarded disposal.
src/devices/Pcd8544/Pcd8544.cs	Clears _controller reference after if/else that may close pins.
src/devices/Pca95x4/Pca95x4.cs	Always clears _controller reference after guarded disposal.
src/devices/Nrf24l01/Nrf24l01.cs	Always clears _gpio reference after guarded disposal.
src/devices/Mpu6xxx9xxx/Mpu9250.cs	Always clears _i2cDevice reference after guarded disposal.
src/devices/Mhz19b/Mhz19b.cs	Always clears _serialPortStream reference after guarded disposal.
src/devices/Mfrc522/Mfrc522.cs	Always clears _controller reference after guarded disposal.
src/devices/Mcp25xxx/Mcp25xxx.cs	Always clears _gpioController reference after guarded disposal.
src/devices/Mcp23xxx/Mcp23xxx.cs	Always clears _controller and _bus references after guarded disposal.
src/devices/LiquidLevel/LiquidLevelSwitch.cs	Always clears _controller reference after guarded disposal.
src/devices/LidarLiteV3/LidarLiteV3.cs	Always clears _gpioController reference after guarded disposal.
src/devices/KeyMatrix/KeyMatrix.cs	Clears _gpioController reference after if/else that may close pins.
src/devices/Ht1632/Ht1632.cs	Always clears _controller reference after guarded disposal.
src/devices/Hcsr501/Hcsr501.cs	Always clears _controller reference after guarded disposal.
src/devices/Hcsr04/Hcsr04.cs	Always clears _controller reference after guarded disposal.
src/devices/GrovePi/GrovePi.cs	Always clears _i2cDevice reference after guarded disposal.
src/devices/ExplorerHat/Motors.cs	Always clears _controller reference after guarded disposal.
src/devices/ExplorerHat/Lights.cs	Always clears _controller reference after guarded disposal.
src/devices/ExplorerHat/Led.cs	Always clears _controller reference after guarded disposal.
src/devices/ExplorerHat/ExplorerHat.cs	Always clears _controller reference after guarded disposal.
src/devices/Dhtxx/DhtBase.cs	Clears _controller reference after if/else that may close pin.
src/devices/DCMotor/DCMotor.cs	Always clears Controller reference after guarded disposal.
src/devices/Common/Iot/Device/Multiplexing/GpioOutputSegment.cs	Always clears _controller reference after guarded disposal.
src/devices/Charlieplex/CharlieplexSegment.cs	Always clears _gpioController reference after guarded disposal.
src/devices/CharacterLcd/LcdInterface.Gpio.cs	Always clears _controller reference after guarded disposal.
src/devices/Ccs811/Ccs811Sensor.cs	Clears _controller reference after if/else that may close pins.
src/devices/Button/GpioButton.cs	Clears _gpioController reference after if/else that may close the pin.
src/devices/Bno055/Bno055Sensor.cs	Always clears _i2cDevice reference after guarded disposal.
src/devices/Bmm150/Bmm150.cs	Always clears _i2cDevice reference after guarded disposal.
src/devices/Blinkt/Blinkt.cs	Always clears _gpioController reference after guarded disposal.
src/devices/Ak8963/Ak8963.cs	Always clears _i2cDevice reference after guarded disposal.
src/devices/Ads1115/Ads1115.cs	Always clears _gpioController reference after guarded disposal.

[krwq]

@copilot open a new PR to fix this

[Copilot]

@krwq I've opened a new pull request, #2587, to work on those changes. Once the pull request is ready, I'll request review from you.