Release gotp v0.6.2 (2025-12-27)

This is the last release for year 2025.

[CHORE]
_doc: merge index into README.
This is so we can serve the _doc/ directory under
https://kilabit.info/project/gotp/ .

[CHORE]
Update minimum Go version to 1.24.0 and update all dependencies.

Happy holidays!
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