Improve performance by fusing kernels

[au2001]

Change Summary

What does this PR change?

It improves performance by 8-12% with these compounding changes:

• aligning mp_number to 2x 16 bytes instead of 8x 4 bytes; and
• merging kernels for iterating/transforming/scoring into a single one

(profanity_inverse is untouched in this PR, so there are still 2 launches total, down from 3-4)

Testing & Verification

How was this tested?

• Unit tests
• Integration tests
• Manual testing (describe steps)
• Verified on staging

I ran the --leading 0 scoring method on different GPUs with the base and head codebase.
For each resulting address, I ran an external verification script which found no mistake.
Here are the results for "70" variant of each NVIDIA generation:

GPU	VRAM	base	head	inverse-multiple	gain
RTX 5070	12 GB	787 MH/s	876 MH/s	-I 393216	+11.3%
RTX 4070	12 GB	659 MH/s	712 MH/s	-I 393216	+8.0%
RTX 3070	8 GB	487 MH/s	536 MH/s	-I 262144	+10.1%
RTX 2070	8 GB	328 MH/s	359 MH/s	-I 16384	+9.4%
GTX 1070	8 GB	201 MH/s	225 MH/s	-I 196608	+12.2%

Edit: Previous results used --benchmark, for which the compiler optimized the kernel by deleting the keccak + scoring. A patch has been added to prevent this from happening.

Notes:
During benchmarks, when reaching speeds of 2-3ms per round, the millisecond clock precision was insufficient.
I thus bumped it to microseconds for increased accuracy.

A bug also prevented from enabling profiling: clCreateCommandQueueWithProperties on OpenCL 2.0+ expects a zero terminated list of name/value pairs, not a bitfield like 1.2 – 0 just so happened to be interpreted as an empty list.

Risk Assessment

Risk Level:

• Low - Minor changes, no operational impact
• Medium - Moderate changes, limited impact, standard rollback available
• High - Significant changes, potential operational impact, complex rollback

Risks & Impact

Fully backwards-compatible with no user-facing changes.
But changes how the kernels work in a non-trivial way.
Requires clearing the cache to see changes (and to rollback).

Disclaimer: this PR was assisted by Claude Opus 5 for code exploration & benchmark scripts.
However, all code being submitted has been hand-written – and I'm a human :)