bugfix - preserve decorated builtin-name calls in inline tests (#677)

[dannymeijer]

Summary

This PR fixes the remaining decorated builtin-name inline-test regression on the v0.3 release branch and folds in the related runner/codegen hardening found during the review loop. Decorated callables such as a source-level sum(...) now shadow implicit builtin roots consistently through typechecking and lowering, multi-file inline-test batches preserve per-file scope without splitting harmless repeated imports, and the v0.3 release notes are decomposed into more readable feature and hardening sections.

Type of change

• Bug fix
• New feature
• Refactor / maintenance
• Documentation
• CI / tooling
• RFC (adds/updates docs/RFCs/*)

Area(s)

Select the primary areas touched (used for review routing; labels are managed separately):

• Incan Language (syntax/semantics)
• Compiler (frontend/backend/codegen)
• Tooling (CLI/formatter/test runner)
• Editor integration (LSP/VS Code extension)
• Runtime / Core crates (stdlib/core/derive)
• Documentation

Key details

• User-facing behavior: Decorated functions whose names overlap builtins resolve to the source binding inside inline tests, and directory inline-test runs keep per-file parser/import scope while still sharing safe batches.
• Internals: Builtin/root dispatch now uses explicit symbol-id backed shadowing checks for stdlib surface functions and surface types, lowering refuses name-based builtin fallback when frontend callee metadata exists, and nested codegen matches modules by explicit path segments before falling back to flat names.
• Risks: The builtin shadowing and test-runner batching paths are compiler hot spots, so the PR includes focused typechecker, integration, snapshot, and full pre-commit coverage. Release-note restructuring is broad but documentation-only.

Testing / verification

• make test / cargo test
• make examples (if relevant)
• incan fmt --check . (if relevant)
• Manual verification described below

Manual verification notes:

• make pre-commit
• cargo test local_function_named --features cli
• cargo test test_decorated_function_named_sum_shadows_builtin_sum_in_inline_module_tests --features cli
• cargo test partition_collision_free_file_groups --features cli
• cargo test module_name_for_segments_disambiguates_join_collisions --features cli
• cargo test std_web_prelude_import_snapshot --features cli --test stdlib_generated_rust_snapshot_tests
• cargo test e2e_inline_decorated_sum_shadows_builtin_sum_issue677 --features cli --test integration_tests
• cargo test e2e_conventional_test_batches_split_import_declaration_collisions_issue676 --features cli --test integration_tests
• cargo test e2e_directory_run_preserves_per_file_inline_test_modules_issue676 --features cli --test integration_tests
• cargo test e2e_fixture_lifetime_success_scenarios_share_one_project --features cli --test integration_tests
• cargo test equivalent_helper_backed_keywords_typecheck --features cli --test integration_tests
• cargo run --quiet --features cli --bin incan -- test /private/tmp/incan-677-repro/src/decorated_sum_union.incn
• git diff --check

Docs impact

• No docs changes needed
• Docs updated
• Docs follow Divio intent (tutorial/how-to/reference/explanation) where applicable

If docs updated:

• Link(s): workspaces/docs-site/docs/release_notes/0_3.md, workspaces/docs-site/docs/roadmap.md

Checklist

• I kept public docs user-focused and moved internals to contributing docs when appropriate
• I avoided duplicating canonical install/run instructions in multiple places
• I added/updated tests where it materially reduces regressions

Closes #677