bugfix - preserve per-file inline test module context (#676)

[dannymeijer]

Summary

This PR fixes directory-level incan test runs for multiple source files that each define one inline module tests: block. The runner now keeps each inline source file as its own generated Rust module, with the generated #[test] harness injected beside that file's declarations. That preserves both parser cardinality and file-local import scope while still batching through one Cargo/libtest harness where the files are compatible. It also bumps the release train to 0.3.0-rc14 and records #676 in the 0.3 release notes.

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: incan test src can now run inline tests from multiple non-test .incn source files without reporting Only one module tests block is allowed per file across the whole directory batch and without Rust E0255 collisions when one inline-tested file imports a public item from another.
• Internals: cross-file inline source batches now generate one Rust module per source file and mark runner-injected entrypoints reachable per module. Ordinary test batches keep the existing root-harness path.
• Risks: this changes the generated harness shape for multi-file inline source batches. The regression now covers file-level consts/statics, models, helper functions, and the InQL-style from functions.columns import col collision shape.

Testing / verification

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

Manual verification notes:

• Reproduced the residual bug - Directory test run treats multiple inline test modules as one file #676 failure before the structural fix: direct file runs passed, while the directory run failed during generated Rust compilation with E0255: the name col is defined multiple times.
• cargo run --quiet --features cli --bin incan -- test <minimal-repro>/src/functions passed with the InQL-style import/public-name collision shape.
• cargo test -p incan --test integration_tests e2e_directory_run_preserves_per_file_inline_test_modules_issue676 -- --nocapture passed.
• cargo test -p incan --test integration_tests e2e_inline_and_imported_surfaces_share_one_project -- --nocapture passed.
• cargo test -p incan cli::test_runner::execution::tests --quiet passed.
• cargo fmt --check passed.
• git diff --check passed.
• make pre-commit passed.

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

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 #676