v0.3.1: Slim verify-only builds via optional Cargo features

A small release that makes the packslip crate's CLI, generator, and signing paths optional Cargo features, so verify-only consumers can pull in a much slimmer dependency graph. packslip remains a work-in-progress proposal with only experimental mise support; the release/v1 format and CLI may still change.

Changed

• The crate is now split into additive Cargo features, all on by default, so the packslip binary and existing dependents are unaffected. A consumer that only verifies a manifest can take the crate with default-features = false, dropping the archive readers, the ELF/Mach-O/PE decoder, the Fulcio/OIDC and minisign signing path, the JSON Schema generator, and the CLI — roughly seventy fewer crates in the dependency graph. (#57, @jdx)

  cargo add packslip --no-default-features

  With defaults off you keep the statement types, verify, verify_release_list, select_artifact, and select_resources. Available features:

  Feature	Adds
  cli (default)	The packslip binary; implies the rest.
  create	Build a statement from built artifacts; implies archive, linkage, sign.
  archive	Read tar and zip archives to resolve declared executable paths.
  linkage	Derive requires.libs from ELF, Mach-O, and PE executables.
  sign	Sign statements, keylessly through Fulcio or with a minisign key.
  manifest	Read a packslip.toml.
  schema	Statement::schema() and ReleaseListStatement::schema().

Full Changelog: v0.3.0...v0.3.1