Remove fused q==8 inverse codelets and use scheduled d3+d3+norm inverse path; simplify twiddle helpers

[falseywinchnet]

Motivation

• Replace fragile, per-ISA fused q==8 inverse codelets with a single, predictable scheduled inverse runner to reduce code size, compiler pressure, and cross-ISA variability.
• Make twiddle lookup codepaths clearer and less branchy in scalar/f32 helpers to avoid nested ternary expressions in hot paths.
• Keep transform math and public APIs unchanged while exposing a linear, forward-like switch schedule for inverse execution to improve portability and predictability.

Description

• Removed/disabled fused q==8 inverse codelets for float and double (previous codelet_d4_inv_f32, codelet_d4_inv, and wide-ISA fused variants) and replaced q==8 handling with explicit two depth-3 codelet calls plus the q==8 norm (d3 + d3 + norm) in all schedule and recursive call sites.
• Rewrote scalar and float twiddle helpers s_twiddle(int) and sf_twiddle(int) to use explicit if branches returning 0 for m==0, C[1]/CF[1] for m==1, and C[m^1]/CF[m^1] otherwise.
• Updated all inverse schedule dispatch sites (rec_inv_res, run_inv_residue_schedule, rec_inv_res for double, and forward scheduling spots) to invoke the two d3 codelets and then norm_q_* for q==8, and removed conditional BRUUN_LEVEL paths that used the fused variants.
• Updated documentation/notes (inverse_acceleration_notes.txt) to record the decision to keep q==8 on the shared d3 + d3 + norm path, list completed changes, and note benchmarking/assembly inspection results.

Testing

• Ran assembly inspection and microbenchmarks for the scheduled inverse on an Intel Xeon Platinum 8370C with -O3 -mavx2 -mfma and native AVX-512 builds, and observed the scheduled inverse running and benchmark output including a direct Inv_ns column. Tests succeeded.
• Performed local build and CI-style compilation across narrow and wide targets (SSE2/NEON, AVX2, AVX-512) to ensure the removed fused codelets did not break builds, and all builds completed successfully.

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Codex Task