[Nextor 3] Fix _GETCLUS copying 64 bytes of data instead of 16

[Konamiman]

"Backport" of #149

Part of #164

[coderabbitai]

📝 Walkthrough

Walkthrough

The pull request modifies the GETCLUS function in MSX-DOS sys.mac by introducing a new entry point with RUN_AND_COPY routing, reducing the buffer copy size from 64 bytes to 16 bytes through updated register operations, and updating the function table linkage to expose GETCLUS publicly.

Changes

Cohort / File(s)	Summary
GETCLUS Function Update source/command/msxdos/sys.mac	Added new GETCLUS entry point routed through RUN_AND_COPY, adjusted buffer copy size from 64 to 16 bytes via register setup (LD C,B; LD B,0), modified copy/stack handling sequence with BC push/pop operations, and exposed GETCLUS as public entry in function table (FNTAB).

Possibly Related Issues

• "Forward-port" Nextor 2 pull requests #164: Directly addresses GETCLUS implementation fixes including routing changes and correction of buffer copy size from 64 to 16 bytes, aligning with the PR's primary modifications.

Poem

🐰 A copy of sixteen hops, not sixty-four,
GETCLUS finds its path through RUN_AND_COPY's door,
With registers aligned and tables made anew,
The rabbit's work brings MSX-DOS through! 🎯

Estimated Code Review Effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and accurately describes the main change: fixing _GETCLUS to copy 16 bytes instead of 64 bytes, which is the core purpose of this PR.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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