Add after-each test hook for hawk

[iethree]

Adds an optional mb.hawk.hooks/after-each hook that runs arbitrary code after each test var, receiving that test's full output and report context, with zero overhead when no hooks are registered.

• New after-each multimethod (mb.hawk.hooks) following the existing before-run/after-run convention. Hooks receive options and a context map: :var, :ns, :report-events (every clojure.test event, each tagged with its :testing-contexts), :output (captured out/err), :summary (pass/fail/error counts), :duration-ms, and :parallel?.
• Zero-cost fast path: registration is checked once per run (after-each-hooks-registered?); with no hooks, run-test adds only a single dynamic-var deref per test — no output/event capture. Capture (a tee'd Writer + per-test event vector) is allocated only when a hook exists, and hooks run lock-free so ^:parallel tests stay concurrent.
• Correct failure attribution: hooks fire just before a var's :end-test-var reaches the reporter, so a hook exception (or a clojure.test assertion inside a hook) is reported as an error/failure attributed to that var — counted in the summary and emitted as a proper element in the JUnit output.
• No default after-each method (it would run once per test); a method on any dispatch value — including :default — enables the feature.
• Adds README docs and tests covering context capture, failing/erroring tests, hook errors, JUnit attribution, the no-hook fast path, and output isolation across concurrent parallel tests.

[Copilot]

Pull request overview

This PR adds an optional mb.hawk.hooks/after-each hook that runs after each individual clojure.test var, enabling consumers to run per-test side effects with access to captured output and report context while keeping a no-hook fast path.

Changes:

• Introduces mb.hawk.hooks/after-each multimethod and after-each-hooks-registered? detection.
• Extends the test runner to (optionally) capture per-test output + report events and invoke after-each before :end-test-var is reported.
• Adds comprehensive tests and README documentation for the new per-test hook behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/mb/hawk/hooks.clj	Adds the after-each hook multimethod and hook-registration detection helper.
src/mb/hawk/core.clj	Implements the optional per-test capture + hook invocation path in the test-var runner.
test/mb/hawk/hooks_test.clj	Adds tests validating context capture, error attribution, parallel behavior, and the no-hook fast path.
README.md	Documents how to register and use after-each per-test hooks and the provided context keys.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.