Lower uninitialized local declarations with Whale initialization tracking #883

Motivation

At fd07427f4a976de05e38eff3ee1760db97fbb761 on Linux amd64 with Rust 1.89 and locked Whale 020d2a4, lexing, parsing and TypedProgram lowering succeed, but calling whale::emit_ir on this source returns Whale backend does not yet support uninitialized locals:

fun main() -> i32 { var x: i32; x = 3; return x; }

Scope

Upstream #243 adds Uninit and initialized-read tracking. After the format-4 integration, lower supported local storage while resetting initialization at each declaration execution, including loop re-entry. Preserve the existing Wave language contract; do not replace uninitialized values with zero or Undef.

Difficulty: hard.

Completion criteria

• Accept declaration followed by a valid assignment/read.
• Preserve initialization/lifetime distinctions across loops and shadowing.
• Verify IR and test available tracked-memory execution without inventing a new Wave policy.

Please mention @LunaStev to discuss the design before starting implementation.

Depends on #868.