chore(v1.14.0): bring intrinsics.rs + phase14 tests under 500-line rule

[petlukk]

Summary

Pre-release hard-rules audit flagged four files over the 500-line limit. This PR fixes all four through extraction (no public API change, 983 tests pass).

File	Before	After
`src/typeck/intrinsics.rs`	665	498
`tests/phase14_tanh_approx.rs`	527	454
`tests/phase14_sin_cos_approx.rs`	509	430
`tests/phase14_log_approx.rs`	501	425

What moved where

Test files — extracted the shared `accuracy_test_impl` (~80 lines per file, structurally identical except for intrinsic name + libm reference + tolerance + padding value) to a parameterized `assert_transcendental_accuracy` helper in `tests/common/mod.rs`. Each phase14 file now imports it and wraps with intrinsic-specific constants.

`intrinsics.rs` — extracted the four transcendental check functions (`check_exp_poly_f32`, `check_tanh_approx_f32`, `check_log_approx_f32`, `check_sin_cos_approx_f32`) to a new `intrinsics_transcendental.rs` sibling. Also moved `check_prefetch` (a self-contained 30-line family) to `intrinsics_prefetch.rs`. Same `impl TypeChecker` block in each sibling, function signatures and visibility unchanged. Follows the established `intrinsics_.rs` pattern (intrinsics_dotprod, intrinsics_pack, intrinsics_neon, etc.).

Context

`intrinsics.rs` was already 546 lines (over the limit) before any v1.14.0 work — that's pre-existing tech debt. The five v1.14.0 feature PRs (#28–#32) added 119 lines and pushed it to 665. The test files I created in those PRs (527 / 509 / 501) were over from inception — that's on me; should have factored the shared helper out the first time.

Test plan

• `cargo test --features llvm --release` — 983 tests pass (same count as before the cleanup)
• Each touched test file independently: all green
• All touched files now under 500 lines (verified by grep)
• No new public API surface (the moved functions keep their `pub(super)` visibility)

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