Fix AppleClang parsing and static initialization

[Jme-Tau]

Summary

Make the parser compile reliably under AppleClang and remove a static-initialization-order dependency exposed by global Tau BDD construction on macOS arm64.

Tracks IDNI/tau-lang#78.

Changes

• copy the predictor set index into a local size_t before comparing it with U.size()
  • avoids AppleClang parsing the dependent it->set < U.size() expression as template syntax
  • does not change parser behavior
• replace inline-static tree and hook mutex objects with function-local static accessors
  • guarantees each mutex is initialized before its first lock
  • avoids pre-main mutex lock failed: Invalid argument aborts when another global initializer calls bintree::get() or create_cache()

Verification

Using AppleClang 17 on arm64 macOS:

• parser static library builds successfully as the Tau submodule
• Tau native Release executable builds and reports version 0.7.0-alpha
• Tau Python 3.14 binding builds and imports
• the combined parser + Tau fix set runs 327 Release tests with no segfaults or aborts

The standalone parser debug-tests and release-tests presets were also attempted. They currently stop in existing char32_t stream tests because libc++ does not provide the required std::ctype<char32_t> / std::numpunct<char32_t> locale facets. That failure is independent of these changes and occurs before the affected parser tests can run.

git diff --check passes.