Fix exponential compilation blowup in pattern matching and boolean simplification

This PR fixes two sources of exponential compilation time:

1. **Boolean expression simplification** (`js_exp_make.ml`):
   The `simplify_and_` function had O(3^n) recursive behavior when
   simplifying nested AND expressions. Added a depth limit (10) to
   prevent exponential blowup while preserving optimizations for
   normal cases.

   Fixes the issue reported in #8039 and #8042 (large unboxed variants).
   Note: PR #8039's diagnosis of "infinite recursion" was incorrect -
   the actual issue was exponential blowup, not infinite loops.

2. **Exhaustiveness checking** (`parmatch.ml`):
   The `exhaust_gadt` function had exponential complexity (~4^n) when
   checking exhaustiveness for dict pattern matching. Added a call
   count limit (1000) that conservatively reports non-exhaustive when
   exceeded, preventing hangs while maintaining correctness.

Performance improvements:
- Large unboxed variants (28 cases): 3.79s -> 0.03s (126x faster)
- Dict pattern matching (6 cases): 0.94s -> 0.04s (24x faster)

Added test cases for both scenarios.

Closes #8074
Closes #8039
Closes #8042

Author: cristianoc