Avoid clearing fresh normalization bitmap

[zachmdsi]

Summary

Avoid clearing the normalization visited bitmap immediately after allocating it.

uset_init() obtains fresh MAP_ANONYMOUS storage, which is already zero-filled. The subsequent uset_clear() touched the entire 512 MiB bitmap before every normal evaluation without changing its contents. This removes that call and the now-unused helper, while documenting the initialization invariant.

Measurements

Measured on an Apple M5 with Apple Clang 21 (clang -O2):

• Trivial program median peak RSS: 538,443,776 B -> 1,605,632 B
• Avoided approximately 32,766 page reclaims per run
• lambda_eval median evaluation time: 1.528 s -> 1.481 s
• cnot_24 median evaluation time: 1.207 s -> 1.201 s

The primary benefit is avoiding a fixed 512 MiB resident-memory cost; timing gains are workload-dependent.

Validation

• ./devs/test/_all_.sh: 217 passed
• Normal-mode differential over all 218 test files: byte-identical output and matching exit behavior
• Identical interaction and heap-allocation counts on measured benchmarks
• Clean builds with -O0, -O2, -O3, and -Os
• Representative normal-form programs passed AddressSanitizer and UndefinedBehaviorSanitizer