chore(release): prepare 1.4.3

[LauraGPT]

Summary

• bump the Python package release contract to 1.4.3
• add the v1.4.3 announcement to all four top-level READMEs
• document the optional Silero VAD adapter and scalable fixed-K diarization path

Verification

• clean-source release suite: 167 passed
• python -m compileall -q funasr
• PEP 517 wheel and sdist build
• twine check on both artifacts
• clean no-dependency wheel install: import, metadata, and CLI version smoke
• runtime wheel smoke with Silero 6.2.1 and fixed-K clustering
• wheel/sdist source diff and package-data verification

Signed-off-by: zhifu gao 18321252+LauraGPT@users.noreply.github.com