Fix collapse clause colon parsing flake

[ouankou]

Issue

• ctest openacc_vv_loop_collapse_force.c occasionally dropped the collapse count, producing collapse(force) instead of collapse(force:2).
• Root cause: the lexer counters (parenthesis/bracket/colon) were left uninitialized and the collapse token did not prime colon_count, so the colon could prematurely end the expression depending on stack garbage.

Solution

• Initialize lexer delimiter/colon counters so expression lexing always starts from a known state.
• Seed colon_count when lexing collapse to allow colon-delimited modifiers (force:2) to remain inside the expression mode.

Testing

• ctest -R "openacc_vv_loop_collapse_force.c" --output-on-failure --repeat-until-fail 200
• ctest --output-on-failure

[ouankou]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🚀

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