regex: \p{...} property classes; interop: the String method surface (cuerdas is green)

\p{L}/\p{Lu}/\p{Ll}/\p{N}/\p{Z}/\p{Ps}/\p{Pe} (+\P negation) land in
both escape positions of the regex compiler, mapped onto the byte PEGs:
ASCII exact, any high byte (inside a UTF-8 sequence) counts as a LETTER —
so ^\p{L}+$ accepts UTF-8 words while \p{N}/\p{Z} stay ASCII. (?u) was
already a tolerated no-op flag. Unknown property names error at compile.

Chasing the acceptance target (cuerdas via deps-conformance) pulled in the
rest of its clj-compat chain, each a real gap:
- the deps-conformance harness reads libraries under clj-compat reader
  features (deps are clj/cljc by definition — without :clj, cuerdas's
  #?(:clj (instance? Pattern x)) branches resolved to NIL bodies)
- instance? knows Pattern/java.util.regex.Pattern (regex values) and
  Character (cuerdas's rx/regexp? gate on split)
- the java.lang.String method surface: .toLowerCase/.toUpperCase/.trim/
  .indexOf(-1 on miss)/.lastIndexOf/.substring/.charAt/.startsWith/
  .endsWith/.contains/.replace/.equalsIgnoreCase/... — ASCII case mapping,
  unknown methods error (the old path silently returned nil)
- the (.method obj args) SUGAR now desugars to (. obj method args) in the
  interpreter — it was never implemented (bare .method heads resolved as
  vars, hence 'Cannot call nil')
- Long/MAX_VALUE / MIN_VALUE statics (f64 approximations)

deps-conformance: medley ok, cuerdas ok (was check-error); dependency now
loads its clj branches and fails only on its single-segment ns resolution.
30 new spec rows (11 regex, 19 interop). Gate exit 0.

test/spec/untested-vars-spec.janet

@@ -129,8 +129,9 @@
   ["delay? true"   "true" "(delay? (delay 1))"]
   ["delay? false"  "false" "(delay? 1)"]
   ["future-call"   "42" "(deref (future-call (fn [] 42)))"]
-  [". member resolves nil" "nil" "(. \"abc\" count)"]
-  [".. threads members" "nil" "(.. \"abc\" count)"])
+  [". calls String surface" "3" "(. \"abc\" length)"]
+  [".. threads members" "\"ABC\"" "(.. \"abc\" toUpperCase)"]
+  ["unknown String member throws" :throws "(. \"abc\" frobnicate)"])
 
 (defspec "untested / protocols: extend + extends?"
   ["extend registers" ":str"