v0.2.0

Macro and protocol mutation, bounded workers and faster repeat runs, from
Mike Hostetler's first community contribution (#1).

• mix covenant.mutate --macros mutates public and private macro bodies and
  their quoted output. Callers named with --recompile are compiled in the
  order given, before the contract tests; list every direct and transitive
  caller, providers first, since discovery isn't automatic. A caller that
  fails to compile makes the mutant invalid, with no kill credit. A
  --recompile path can't name a mutation target, even through a symlink.
• Literal defimpl bodies are mutated. Shared implementation and macro owners
  are kept for ownership and survivor matching.
• Caller and test binaries are restored exactly, and generated and in-memory
  modules are cleaned after the baseline, each mutant and the final check.
• --max-runtime MS bounds the whole job (default one hour), and SIGTERM
  cancels it. Each verdict is saved atomically, so a failed or cancelled job
  keeps its partial results, and never passes as a complete matrix.
  --max-mutants-per-worker N retires a worker after N verdicts (default 50),
  once the original suite passes on it, and a fresh VM takes the rest.
• --only runs chosen mutation IDs without renumbering them or claiming full
  coverage. --fail-fast keeps partial credit for kills. --prioritize PATH,
  which requires --fail-fast, tries a test that killed the same mutant in an
  earlier matrix first.
• --checkpoint and --resume DIR (MIX_ENV=test only) keep only verified,
  completed worker groups, fingerprinted against source, fixtures, config,
  dependencies, BEAMs and options. A resumed run always takes a fresh baseline.
• --selective-recompile, with --macros, measures compile-time dependencies
  and recompiles only the affected callers.
• Progress shows the baseline and elapsed worker time. Final reports use
  run-specific temporary files, so concurrent runs don't remove each other's.
• Cleanup and selective dependency tracing need OTP 27 or later.