fix: return consistent response format for TIMESTAMP command

[fank]

Summary

• Change :TIMESTAMP: to return ["ok", "timestamp"] instead of raw number
• Aligns with the response format used by all other extension commands

Test plan

• Build DLL and test :TIMESTAMP: returns ["ok", "1234567890"] format
• Verify existing SQF code handles the new format

[github-actions]

Merging this branch will not change overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/OCAP2/extension/v5/pkg/a3interface	0.00% (ø)

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Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/OCAP2/extension/v5/pkg/a3interface/rvextension.go	0.00% (ø)	0	0	0

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.