Build provenance for Homebrew: January 2024

Logistical note: This update also contains updates from December.

Completed

We've merged initial attestation generation support into homebrew-core, meaning that all new bottle builds/uploads are being accompanied by build provenance: Homebrew/homebrew-core#160941
We've made changes to Homebrew's build workflows to enabled build provenance generation: Homebrew/homebrew-core#160941
We performed a earlier provenance generation test on Homebrew/actions: Homebrew/actions#479
We completed API-level DSSE signing support in sigstore-python: sigstore/sigstore-python#804
We have continued to perform refactoring and cleanup tasks on sigstore-python in support of DSSE signing and verification: sigstore/sigstore-python#862
We've submitted API improvements to python-betterproto in preparation for integrating betterproto into in_toto_attestations: danielgtaylor/python-betterproto#551
We've made code quality, CI/CD, and API improvements to in_toto_attestations: in-toto/attestation#311, in-toto/attestation#312, in-toto/attestation#306, in-toto/attestation#301

We are investigating the second stage of build provenance generation for homebrew-core ("backfill" attestations for pre-existing bottles)
We are beginning work on a brew subcommand for build provenance generation: Homebrew/brew#16543
We are continuing work on support for betterproto in in_toto_attestations: in-toto/attestation#315
We are continuing refactor and standards work in support of DSSE verification in sigstore-python: sigstore/sigstore-python#876, sigstore/sigstore-conformance#122