Update documentation: p4python 2025.2 fixes GIL blocking in connect()

[Copilot]

The GIL blocking issue in connect()/aconnect() was fixed in p4python 2025.2 per release notes. The prominent warning is no longer warranted.

Changes

• README.md: Replaced "Caveats" section with footnote recommending p4python 2025.2+ for optimal async performance
• CHANGELOG.md: Documented the documentation update in Unreleased section

The note still informs users about the historical issue but doesn't dominate the documentation. No code changes required—no comments referenced this caveat.

Original prompt

The readme mentions a Caveat about connect/aconnect. The underlying bug was fixed in perforce p4python release 2025.2, as per the following:
https://filehost.perforce.com/perforce/r25.2/doc/user/p4pythonnotes.txt
Please update the readme, and any comment in the file. This needs no longer be a prominent warning, maybe just a footnote, to use 2025.2 or later to avoid blocking connect().
Similarly, if there are any comments in code, they can be similarly removed, or changed.

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