test+docs: spec coverage for migratus-enablement fixes; list migratus

Adds spec/conformance coverage for everything landed enabling migratus:
- conformance corpus (runs interpret/compile/self-host): def 3-arg docstring,
  def/defn ^{:map} name meta, defmacro arity-clause + docstring, defmulti
  docstring, assoc-nil/assoc-in real maps, try multi-body + finally-on-success,
  current-ns restore after a caught throw, cross-ns methods visibility.
- spec suites: host-interop (exception ctors, Character/Thread/Long, Timestamp/
  SimpleDateFormat, java.io.File model + File-aware file-seq, clojure.tools.logging),
  regex (Pattern statics + MULTILINE + quote, String .matches/.replaceAll/
  .replaceFirst), maps (assoc on nil), multimethods (defmulti docstring +
  value-based methods/get-method), macros (defmacro arity-clause + name meta).

Rewrote clojure.tools.logging/spy as a single variadic arity (jolt defmacro
takes only the first clause of a multi-arity macro — jolt-q8l).

docs/libraries.md: add migratus and the next.jdbc compatibility layer, with the
janet-lang/sqlite3 int64 caveat for 14-digit timestamp ids.

Full gate green; conformance 350/350 x3 modes.

docs/libraries.md

@@ -20,3 +20,13 @@ Libraries confirmed to load and pass their conformance checks on Jolt
   (select/insert/update/delete/joins/:inline), loaded unmodified from git
 * [clojure.jdbc](https://github.com/yogthos/clojure.jdbc) — as [jolt-lang/db](https://github.com/jolt-lang/db)'s
   `jdbc.core`, reimplemented over janet sqlite3/pq drivers (SQLite + PostgreSQL)
+* [next.jdbc](https://github.com/seancorfield/next-jdbc) — a compatibility layer in
+  [jolt-lang/db](https://github.com/jolt-lang/db) (`next.jdbc`, `next.jdbc.sql`,
+  `next.jdbc.prepare`, `next.jdbc.transaction`) over `jdbc.core`, for libraries
+  that target the next.jdbc API
+* [migratus](https://github.com/yogthos/migratus) — database migrations; loads
+  unmodified and runs filesystem SQL/EDN migrations against SQLite through the
+  next.jdbc layer above. `migrate`/`rollback` round-trip end to end. Caveat:
+  migration ids are 14-digit timestamps, and the janet-lang/sqlite3 driver
+  currently truncates INTEGER columns to 32 bits, so completion tracking needs
+  the one-line upstream fix (`sqlite3_column_int64`); ids under 2^31 work as is.