feat(assail): strip #[cfg(test)] mod bodies before Rust keyword scan

Closes the two residual UnboundedAllocation false positives classified
in 007-lang/audits/audit-unbounded-allocation.md §5 and §6:

  - crates/oo7-core/src/backends_tier4.rs — test fn
    `choreography_unbounded_loop` inside `#[cfg(test)] mod tests {}`
  - crates/oo7-core/src/metacompiler.rs — test fn
    `validate_detects_left_recursion` inside the same shape

Both files are production Rust but embed a `#[cfg(test)] mod tests
{ … }` at the bottom. Previously, substring-based dangerous-pattern
checks on `code_only` saw the test-fn identifiers (`unbounded`,
`recursion`) and flagged the whole file as UnboundedAllocation. The
file-path-based `is_test_file` predicate does not recognise inline
test modules, so those tokens counted against the production file.

Fix: add `strip_cfg_test_modules_rs(&code_only)` and use the
resulting `code_no_test_mods` for the unbounded-allocation keyword
check. This is the Rust analogue of `count_unsafe_in_test_blocks` on
the Zig side. Intentionally scoped to the unbounded-allocation
check only — broader application to unsafe/panic/crypto checks is
deferred to keep blast radius small.

Recognised attribute forms: `#[cfg(test)]`, `#[cfg(any(test, …))]`,
`#[cfg(all(test, …))]`, and any other `cfg(…)` whose argument list
contains bareword `test` outside a `not(test)` group.
`#[cfg(not(test))]` is production-only and left in place.

New helpers:
  - `Analyzer::strip_cfg_test_modules_rs(content)` — brace-match
    `#[cfg(test)] mod <name> { … }`, replace body with whitespace,
    preserve line count so downstream line numbers stay stable.
  - `Analyzer::cfg_args_select_test(args)` — classify the argument
    list of `#[cfg(...)]` as selecting for `test` or not.
  - `strip_not_test_groups(args)` — erase `not(test)` groups so
    `all(not(test), …)` does not mis-classify.

Tests: 15 new unit tests covering the common attribute forms,
pub mod, mod without body, nested braces, `feature = testable`
substring non-matches, and `not(debug_assertions)` preservation.
All 182 lib tests pass (was 167 + 15 new = 182).

Measured impact on 007-lang: UnboundedAllocation residuals 6 → 4.
Remaining 4 are all legitimate `std::fs::read_to_string` full-file
reads of operator-supplied input (CLI, import resolver, diagnostics
temp file, config loader) and are accepted in the audit doc.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath