Stage 2 of parser study: recursive-descent parser that builds an AST
from the token stream. Handles static function calls, dynamic/computed
calls (DynCall), eval brackets, brace groups, and nested arglists.
Enhanced tokenizer with full L2 %-substitution coverage. Added test
corpus covering all major expression patterns.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
