Add local version identifier to package metadata for pre-built wheels

[yundai424]

This attempts to fix #730 so that we're following PEP 440

Currently the filename of pre-built wheels (published by GH Action in each release) follows the public+local versioning scheme as suggested in PEP 440 local version identifier section, but this is NOT reflected in the actual package metadata (PEP 459) and this causes discrepancy. For example, if these wheels are uploaded to a private python index, for instance a hosted python index within a company, people can't specify the exact version to install by simply using pip install flash-attn===2.4.2+<local version>

[yundai424]

@tridao wondering if you would mind helping take a look at this change and see if it can be merged. Thanks!

[yundai424]

@tridao @piercefreeman @ksivaman et al. would greatly appreciate your help to take a look at this. Thanks!