core: #inst instant values + syntax-quote literal collapse (spec 2.3/2.4)

#inst (jolt-rnh): an instant is an immutable tagged struct
{:jolt/type :jolt/inst :ms <epoch-millis>} — equality and map-key hashing by
INSTANT, so different offsets denoting the same moment are =. The reader
parses RFC3339 with Clojure's partial-timestamp defaults (#inst "2020" is
2020-01-01T00:00:00.000Z) and errors on malformed input; inst?/inst-ms in
the overlay; pr-str prints the canonical
#inst "yyyy-MM-ddThh:mm:ss.fff-00:00" and round-trips; str gives the bare
RFC3339 string. Self-evaluating in the evaluator (like uuid/chars).

Syntax-quote (jolt-l2a): a syntax-quoted self-evaluating literal (string,
number, boolean, nil, keyword, char) collapses to the literal at READ time,
matching Clojure's reader — so nested/adjacent backticks over literals are
inert: (= "meow" ```"meow") is true (jank pass-adjacent). Symbols still
qualify and collections still template. General nested syntax-quote over
non-literals remains UNVERIFIED in spec S25.

Tests: inst-spec (18 cases incl. partial defaults, offsets, round-trip),
+10 literal-collapse reader rows, +5 conformance rows (321x3). Spec
02-reader S20/S25 updated to normative. Suite stable 4470/86.

test/integration/conformance-test.janet

@@ -193,6 +193,13 @@
    ["macroexpand"        "true"  "(= (quote if) (first (macroexpand (quote (when-not false 1)))))"]
    ["require bare symbol" "\"a,b\"" "(do (require (quote clojure.string)) (clojure.string/join \",\" [\"a\" \"b\"]))"]
    ["ns-publics lookup"  "true"  "(do (def cnp 7) (some? (get (ns-publics (quote user)) (quote cnp))))"]
+
+   ### ---- #inst + syntax-quote literal collapse (spec 2.4/2.3) ----
+   ["inst? + inst-ms"    "0"     "(inst-ms #inst \"1970-01-01T00:00:00Z\")"]
+   ["inst partial = full" "true" "(= #inst \"2020\" #inst \"2020-01-01T00:00:00Z\")"]
+   ["inst offset normalized" "true" "(= #inst \"2020-01-01T01:00:00+01:00\" #inst \"2020-01-01T00:00:00Z\")"]
+   ["sq literal collapse" "true" "(= \"meow\" ```\"meow\")"]
+   ["sq number collapse"  "42"   "``42"]
    ["macroexpand-1 when" "2"     "(count (rest (macroexpand-1 (quote (when true 1)))))"]
 
    ### ---- HIGH: aliased namespace calls ----