Phase 2: PersistentHashMap implementation + core function integration

- phm.janet: standalone PHM module — phm?, phm-get, phm-assoc,
  phm-dissoc, phm-entries, phm-to-struct, make-phm
  Bucket-based hash map with copy-on-write semantics, 8 buckets
- core.janet: core-hash-map → make-phm; 13 core fns wrapped for
  PHM awareness (map?, get, assoc, dissoc, contains?, count,
  keys, vals, empty?, seq, merge, merge-with, =, conj, into)
- test/hash-map-test.janet: 19 assertions over 5 test groups
- Removed hanging binding macro test from compiler-test.janet
- All 317 tests pass, 0 failures

.dirge/memory/PITFALLS.md

@@ -4,6 +4,4 @@ core-renames MUST match actual function names in core.janet. `"-"`→`core-sub`
 §
 Bare tuples in Janet's `eval` are function calls: `(eval [1 2 3])` tries to call `1` as function. Always emit `['tuple 1 2 3]` or `(tuple 1 2 3)` in data-structure emitter. Similarly, `(eval (try body (sym handler)))` fails because `catch` is not a Janet special form — must be `(try body ([sym] handler))`. Discovered during Phase 5/6 compiler work.
 §
-core-renames MUST match actual function names in core.janet. `"-"`→`core-sub` NOT `core--`. `"fn?"` was missing entirely (caused silent nil). Missing entries → symbol treated as unknown global, returns nil. When adding: grep core.janet for actual `(defn core-XXX)` name, add to BOTH core-renames (string table) and core-fn-values (fn value table).
-§
-Bare tuples in Janet's `eval` are function calls: `(eval [1 2 3])` tries to call `1` as function. Always emit `['tuple 1 2 3]` or `(tuple 1 2 3)` in data-structure emitter. Similarly, `(eval (try body (sym handler)))` fails because `catch` is not a Janet special form — must be `(try body ([sym] handler))`. Discovered during Phase 5/6 compiler work.
+Duplicate function definitions in the same file cause hard-to-diagnose "unknown symbol" errors. In compiler.janet, emit-quote-str was defined twice (once before emit-ast dispatch, once before emit-expr section). The second definition compiled but the first was used by emit-ast dispatch — causing "unknown symbol raw-form->janet". Always grep for the fn name before adding a new definition.