Remove source_code from node location

[0xGeorgii]

Closes #69

[codecov]

Codecov Report

❌ Patch coverage is 28.38710% with 111 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
core/ast/src/arena.rs	11.94%	59 Missing ⚠️
core/type-checker/src/type_checker.rs	32.85%	47 Missing ⚠️
core/ast/src/nodes.rs	28.57%	5 Missing ⚠️

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[Copilot]

Pull request overview

This PR removes the source_code field from the Location struct to optimize memory usage and improve performance. The source text is now stored once in SourceFile.source instead of being duplicated in every node's location.

Changes:

• Removed source: String field from Location struct and made it Copy
• Added source: String field to SourceFile to store the complete source text
• Replaced Vec<NodeRoute> with FxHashMap for O(1) parent/child lookups in the Arena
• Added convenience methods get_node_source() and find_source_file_for_node() to the Arena API

Reviewed changes

Copilot reviewed 14 out of 15 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
core/ast/src/nodes.rs	Removed source field from Location, added Copy derive, and added source field to SourceFile
core/ast/src/builder.rs	Updated to store source in SourceFile instead of each Location
core/ast/src/arena.rs	Replaced linear parent lookup with hash map, added source text retrieval methods
core/ast/src/nodes_impl.rs	Updated SourceFile::new() to accept source parameter
core/type-checker/src/type_checker.rs	Removed .clone() calls on Location (now uses Copy)
core/type-checker/src/errors.rs	Removed source field from test location construction
tests/src/ast/nodes.rs	Updated tests to remove source parameter, added comprehensive Copy tests
tests/src/ast/builder.rs	Added extensive tests for source retrieval and location offsets
tests/src/ast/arena.rs	New file with comprehensive tests for Arena parent/child lookup and source retrieval
tests/src/type_checker/type_info_tests.rs	Updated dummy_location() to remove source parameter
CONTRIBUTING.md	Minor grammar and formatting corrections
CHANGELOG.md	New file documenting all changes in the project
core/ast/README.md	New comprehensive documentation for the AST crate

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