v4.27.0

• Fingerprint a project by what Lake compiles, not by everything beside the
  lakefile. The workspace digest that keys header snapshots and provenance now
  hashes lakefile.toml/lakefile.lean, lean-toolchain, lake-manifest.json,
  and the .lean files under each declared target's module roots (the whole
  tree, minus .git and .lake, when the lakefile is not declarative).
  Previously every byte under the project root was read on each check and
  build, so a lakefile above a data directory, a virtual environment, or an
  unrelated monorepo made the first step of a check run for minutes with no
  output. Digests change value once because of this.
• Announce project fingerprinting as project.fingerprint_started and
  project.fingerprint_finished events (phase fingerprint, with
  elapsed_ms), so --verbose never goes silent between check.started and
  the first Lake invocation.