fix(python): declare init_dwt_band_d to Cython as adm.c defines it

[lusoris]

BLUF: the Python harness wheel failed to build on every hosted job that builds it, because adm_dwt2_cy.pyx declared init_dwt_band_d() with the signature adm.c had before #1859. The declaration and the call are fixed; a device-free contract test keeps them in step.

Cause

#1859 changed core/src/feature/adm.c::init_dwt_band_d() from char *init_dwt_band_d(band, char *data_top, size_t buf_sz_one) (cursor in bytes) to double *init_dwt_band_d(band, double *data_top, size_t band_len) (cursor in samples). compat/python-vmaf/core/adm_dwt2_cy.pyx text-includes adm.c, re-declares the helper, and kept the old declaration, so the generated adm_dwt2_cy.c:21871 passes char * as double *. Failing jobs: Ubuntu clang, Ubuntu ARM clang, macOS clang, macOS clang+DNN (run 37051927171, jobs 110987165105, 110987165289, 110987165189, 110987165152). The error is -Wincompatible-pointer-types as an error on clang 22 and Homebrew clang; GCC rejects it too. No warning flag is touched.

Reproduction

Before: cd python && CC=clang python setup.py build_ext (also CC=gcc):
../compat/vmaf/core/adm_dwt2_cy.c:21871:58: error: incompatible pointer types passing 'char *' to parameter of type 'double *' [-Wincompatible-pointer-types] (and :21871:20, assigning to char * from double *).
After: both compilers build vmaf.core.adm_dwt2_cy clean. The generated code is architecture-independent, so the aarch64 job fails and passes for the same reason (no qemu run).

Fix: double *data_top, data_top = data_buf, declaration double *init_dwt_band_d(adm_dwt_band_t_d *band, double *data_top, size_t band_len), call with buf_sz_one // sizeof(double) (the byte plane size to a sample count, as the C caller does).

Test: core/test/test_cython_adm_dwt_band_decl_contract.py (fast suite, no compiler, no Cython) compares the declaration with the definition and the call's length; it fails 3 of 4 cases on the old .pyx and passes 4 of 4 now.

make test-netflix-golden: 271 passed, 12 skipped.

Checklist

• Research digest — no digest needed: a stale declaration after a signature change.
• Decision matrix — no alternatives: only-one-way fix (the declaration must match the definition).
• AGENTS.md invariant note — no rebase-sensitive invariants beyond the rebase note.
• Reproducer / smoke-test command — see Reproduction.
• CHANGELOG fragment — changelog.d/fixed/cython-adm-dwt-band-declaration.md.
• Rebase note — docs/rebase-notes.md.
• state.md — T-CI-MASTER-FIRST-FULL-RUN-2026-10-02, item 9.
• User-discoverable docs — not applicable: no user-visible surface changes.
• ADR — not applicable: bug fix.
• Netflix golden gate — run, 271 passed, 12 skipped; no assertion touched.