fix(assembly): correct AMD64 AVX2 stack frame offsets

[shaia]

Fix critical assembly bugs that caused go vet failures and test failures on Linux and Windows.

Changes:

• bucket_lookup_avx2_amd64.s: Fix frame size from /bin/zsh-25 to /bin/zsh-33
  • Correct return offset from ret+25(FP) to ret+32(FP)
• batch_avx2_amd64.s: Fix frame size from -72 to -64
  • Correct results_base offset from +32(FP) to +24(FP)
  • Correct fingerprintBits offset from +56(FP) to +48(FP)
  • Correct numBuckets offset from +64(FP) to +56(FP)

The errors were due to incorrect calculation of Go function argument sizes:

• []byte = 24 bytes (base + len + cap, each 8 bytes)
• byte = 8 bytes (aligned)
• bool = 8 bytes (aligned)

All tests now pass with race detector enabled on all platforms.

Fixes: go vet errors on AMD64
Fixes: TestBucketLookup* failures on Linux and Windows
Fixes: XXHash batch processing on all platforms

[Copilot]

Pull Request Overview

This PR fixes critical assembly bugs in AMD64 AVX2 implementations that caused go vet failures and test failures on Linux and Windows. The changes correct stack frame sizes and argument offsets in two assembly files.

Key Changes:

• Corrected return value offsets in bucket_lookup_avx2_amd64.s from +25 to +32
• Fixed frame size and all argument offsets in batch_avx2_amd64.s from incorrect values to proper 8-byte aligned offsets
• However, the frame size in bucket_lookup_avx2_amd64.s still appears to be incorrect (should be 40, not 33)

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
internal/lookup/bucket_lookup_avx2_amd64.s	Partially corrected frame size to 33 and return offsets to 32; however, frame size should be 40 based on argument layout
internal/hash/xxhash/batch_avx2_amd64.s	Correctly fixed frame size to 64 and adjusted all argument offsets (results_base, fingerprintBits, numBuckets) to proper aligned values

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[Copilot]

The frame size should be 40, not 33. The function has:

• fingerprints []byte = 24 bytes (3 × 8-byte words at offsets 0, 8, 16)
• target byte = 8 bytes (aligned, at offset 24)
• return bool = 8 bytes (aligned, at offset 32)

Total = 40 bytes (5 × 8-byte slots)

The correct declaration should be TEXT ·bucketLookupAVX2(SB), NOSPLIT, $0-40

Suggested change

	TEXT ·bucketLookupAVX2(SB), NOSPLIT, $0-33
	TEXT ·bucketLookupAVX2(SB), NOSPLIT, $0-40