PEP 751: Support `attestation_identities` in generated lockfiles.

[di]

What's the problem this feature will solve?

Currently, outputting attestation-identities in a PEP 751 lock file is not supported:

https://github.com/pypa/pip/blob/c46141c29c3646a3328bc4e51d354cc732fb1432/src/pip/_internal/models/pylock.py#L91C23-L91C45

Describe the solution you'd like

Generated lockfiles should include the attestation-identities array per PEP 751.

Alternative Solutions

n/a

Additional context

n/a

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[webknjaz]

FYI, there's https://github.com/trailofbits/pylock-attestations for injecting them. Could be used a prior art or a vendored integration.

cc @facutuesca @woodruffw