fix(agc): size CMASK by whole 1024x512 metablocks

[oneandonlydean]

What

Sizes a color target's CMASK in whole 4 KiB metablocks of 1024x512 pixels, instead of one packed nibble per 8x8 tile. This is commit 1c84890 from #1237 on its own, by its author; #1072 landed without it.

Why

#1072 checks and expands cmaskBytes (State.cpp) bytes of CMASK, one nibble per 8x8 tile from the start of the target. The nibbles are swizzled inside 4 KiB metablocks of 1024x512 pixels, so the CMASK of a 1920x1080 target spans 0x6000 bytes (the size titles clear), not 16200. The lower-right tiles lie past the packed size, so the all-cleared check doesn't look at them and the expanded store leaves them fast-cleared.

Tested

• cmaskTests in tests/Graphics.cpp checks CmaskBytes for 1920x1080 (0x6000), 960x544, 800x450, 1024x512 and 3840x2160, and runs the fast-clear passes over a whole 4 KiB CMASK.
• The same commit, as part of fix(agc): size CMASK by whole 1024x512 metablocks #1237 on top of feat(agc): render into CMASK fast-clear color targets #1072, passed game runs with no visual or FPS regression.
• CI on this PR.

Checklist

• Based on current main; no other open PR implements the same functions
• One topic per PR; follow-ups go in a new PR
• No comments in code except technical debt
• Unimplemented paths throw (NotImplemented_nid_no_patch); silent stubs are listed in TechnicalDebt
• No notes, investigation .md files or images added to the repository (attach them to this PR)
• New third-party code is a submodule built from source
• Generic behaviour, not specific to one title
• Depends on: none (follow-up to feat(agc): render into CMASK fast-clear color targets #1072; the same commit is in fix(agc): size CMASK by whole 1024x512 metablocks #1237)
• AI-assisted: yes

[github-actions]

Other open pull requests touch the same code. Merging one will break the other, or both implement the same thing. If this one builds on them, list them in Depends on.

Pull request	Conflicting files (lines on main)	Same exports	Same new files
#1346	core/libs/prx/libSceAgcDriver/Graphics/include/State.hpp L104 core/libs/prx/libSceAgcDriver/Graphics/src/State.cpp L633