feat: precise file:line:col source locations for type errors (jolt-fqy)

RFC 0006 error reporting wanted file:line:col but IR nodes carried no
position, so diagnostics read only "type error in <ns>: <msg>". Now:

    type error /tmp/scene.clj:5:5: `inc` requires a number, but argument 1 is a string

The reader records each LIST form's absolute start offset in a table keyed
by form identity (lists are fresh arrays, never interned), gated behind a
flag the loaders enable only when JOLT_TYPE_CHECK is on — zero cost off.
Keying by identity makes positions survive macroexpansion exactly when the
user's own sub-form is spliced through, and absent for macro-synthesized
structure: a `(inc :k)` written inside `(when c ...)` reports at its own
line, never at the expansion's generated if/do.

The analyzer stamps the offset onto :invoke nodes (form-position host
contract fn); the checker carries it into each diagnostic as :pos; the
loaders stash the file's source + path on the env (save/restored across
nested requires); backend/type-check! converts offset -> line:col via the
reader's line-col and renders the RFC format. Falls back to the ns when no
position is available (synthetic forms), so it is never worse than before.

Gate green, conformance 335/335, suite 4718, runtime bench even (positions
are compile-time only; off by default).

jolt-core/jolt/analyzer.clj

@@ -23,7 +23,7 @@
                                form-map-pairs form-set-items form-special? compile-ns
                                form-macro? form-expand-1 resolve-global
                                form-sym-meta host-intern! form-syntax-quote-lower
-                               record-type?]]))
+                               record-type? form-position]]))
 
 (declare analyze)
 
@@ -250,8 +250,13 @@
           (and (form-sym? head) (not shadowed) (form-macro? ctx head))
             (analyze ctx (form-expand-1 ctx form) env)
           :else
-            (invoke (analyze ctx head env)
-                    (mapv #(analyze ctx % env) (rest items))))))))
+            ;; stamp the list form's source offset onto the :invoke (jolt-fqy)
+            ;; so the success checker can report file:line:col. nil when the
+            ;; reader did not record it (synthetic/macro-built forms).
+            (let [n (invoke (analyze ctx head env)
+                            (mapv #(analyze ctx % env) (rest items)))
+                  p (form-position form)]
+              (if p (assoc n :pos p) n)))))))
 
 (defn analyze
   ([ctx form] (analyze ctx form (empty-env)))