Add ivar support to flow sensitive typing

[apiology]

Adds support for doing flow-sensitive typing in instance variables, not just local variables.

Note: This approach assumes single-threaded use for type-checking purposes - it's possible to be clever and subvert it, but as a way to reduce false positives in nil-checking, it seems very effective.

Builds on:

• Union type enforcement castwide/solargraph#1127

[apiology]

@copilot review

[Copilot]

@apiology I've opened a new pull request, #20, to work on those changes. Once the pull request is ready, I'll request review from you.

[Copilot]

Pull Request Overview

This PR adds support for instance variables (ivars) to flow-sensitive typing. Previously, flow-sensitive typing only handled local variables (lvars), which limited type narrowing in conditional expressions. The implementation tracks instance variables similarly to local variables, enabling proper type inference for patterns like !@foo.nil? && @foo.upcase.

Key changes:

• Extended FlowSensitiveTyping class to track and process instance variables alongside local variables
• Modified node processors to thread an ivars array parameter alongside the existing locals parameter
• Updated InstanceVariable chain resolution to use var_at_location for flow-sensitive type selection

Reviewed Changes

Copilot reviewed 30 out of 30 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
lib/solargraph/parser/flow_sensitive_typing.rb	Core logic updated to handle ivars in addition to lvars for type narrowing
lib/solargraph/parser/node_processor.rb	Added ivars parameter to process method signature and return type
lib/solargraph/parser/node_processor/base.rb	Added ivars reader and updated constructor to accept ivars parameter
lib/solargraph/parser/parser_gem/class_methods.rb	Modified map method to handle ivars in return value
lib/solargraph/parser/parser_gem/node_processors/*.rb	Updated all node processors to thread ivars parameter through processing
lib/solargraph/source/chain/instance_variable.rb	Updated resolve method to use var_at_location for flow-sensitive ivar resolution
lib/solargraph/library.rb	Removed obsolete @sg-ignore comments for ivar handling
lib/solargraph/pin/*.rb	Removed redundant methods and obsolete flow-sensitive typing comments
lib/solargraph/type_checker/rules.rb	Updated todo count for flow-sensitive typing improvements
spec/type_checker/levels/strong_spec.rb	Added comprehensive tests for ivar flow-sensitive typing
spec/type_checker/levels/alpha_spec.rb	Removed pending tests that are now covered
spec/source/chain/instance_variable_spec.rb	Updated tests to include location parameters
spec/parser/flow_sensitive_typing_spec.rb	Added test for ivar nil check pattern
.rubocop_todo.yml	Updated exclusions to reflect code cleanup

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