test: adapt jank's form/reader tests into spec suites; fix case no-match

Vendoring jank's behavior (not the project): we base our own copies on the
jank test corpus to close coverage gaps, but maintain them ourselves since
jank may diverge. Two new spec batteries (jank-isms translated to Jolt:
letfn* -> letfn, jank catch types -> :default; platform-specific bigdec/
biginteger/ratio/uuid/##Inf/unicode cases omitted):

- test/spec/forms-spec.janet (52): case, fn (arity/variadic/closure/recur/
  named), let, letfn, loop, try, if/do/def/call — incl :throws regression
  cases (no-match, bad params, nil call).
- test/spec/reader-forms-spec.janet (22): #() (% %N %&), #' var-quote,
  ^metadata, syntax-quote (gensym/unquote/splice).

Fix surfaced by adaptation: case with no matching clause and no default now
throws 'No matching clause' (Clojure semantics) instead of returning nil
(00-syntax). Gate green incl full jpm build+test.

Other gaps the adaptation surfaced are filed (tests adjusted to jolt's
current behavior + a comment, not silently dropped):
  jolt-vdo case duplicate test constants not rejected
  jolt-w2v loop bindings not sequential (later init can't see earlier)
  jolt-6x1 #() %& miscomputes arity with a higher positional (%2 …)
  jolt-xl0 ^meta not attached to collection literals ({}/[]/#{})
  jolt-265 syntax-quote doesn't fully-qualify core syms to clojure.core/
  jolt-edb syntax-quote ~/~@ not processed inside set literals

test/spec/reader-forms-spec.janet

@@ -0,0 +1,45 @@
+# Specification: reader forms + syntax-quote + metadata.
+#
+# Adapted from the jank test corpus (test/jank/{syntax-quote,metadata,reader-macro,
+# call}); we keep our own copies since jank may diverge. Syntax-quoted symbols are
+# qualified to clojure.core (matching jank/Clojure). Platform-specific reader forms
+# (#uuid, #inst, ##Inf/##NaN, bigdecimal/biginteger/ratio) are omitted.
+(use ../support/harness)
+
+(defspec "reader / anonymous fn #()"
+  ["no args"         "3"      "(#(+ 1 2))"]
+  ["one arg %"       "6"      "(#(* % 2) 3)"]
+  ["positional %1 %2" "[1 2]" "(#(do [%1 %2]) 1 2)"]
+  ["rest %&"         "[1 2 3]" "(#(do %&) 1 2 3)"]
+  ["fixed + rest"    "[2 3]"  "(#(do % %&) 1 2 3)"])
+  # gap (jolt-6x1): %& with a higher positional (e.g. #(do %2 %&)) miscomputes the
+  # fixed arity — (#(do %2 %&) 1 2 3) yields (2 3), should be [3] (rest after %2).
+
+(defspec "reader / var-quote #'"
+  ["var-quote = var" "true"   "(= (var str) #'str)"]
+  ["is a var"        "true"   "(var? #'str)"]
+  ["deref var-quote" "5"      "(do (def w 5) (deref #'w))"])
+
+(defspec "reader / metadata ^"
+  ["meta on quoted sym" "true" "(:foo (meta (quote ^:foo bar)))"]
+  ["with-meta map"   "true"   "(:k (meta (with-meta {} {:k true})))"]
+  ["with-meta vector" "true"  "(:k (meta (with-meta [] {:k true})))"]
+  ["non-metadatable num" "nil" "(meta 100)"]
+  ["non-metadatable str" "nil" "(meta \"\")"]
+  ["non-metadatable bool" "nil" "(meta true)"])
+  # gap (jolt-xl0): ^meta on collection literals ({}/[]/#{}) isn't attached —
+  # (meta ^:foo {}) is nil; symbol meta + (with-meta …) work.
+
+(defspec "reader / syntax-quote"
+  ["plain literal"   "[1 2 3]" "`[1 2 3]"]
+  ["gensym distinct" "true"   "(not= `meow# `meow#)"]
+  ["gensym stable"   "true"   "(let [s `[meow# meow#]] (= (first s) (second s)))"]
+  ["qualifies unresolved" "(quote user/foo)" "`foo"]
+  ["unquote value"   "[1 2 3]" "(let [a [1 2 3]] `~a)"]
+  # functional: the syntax-quoted call evaluates correctly (jolt-265: core syms are
+  # left bare rather than qualified to clojure.core/, but still resolve at eval).
+  ["unquote call evals" "6" "(let [a 5] (eval `(+ ~a 1)))"]
+  ["splice call evals" "6"  "(let [a [1 2 3]] (eval `(+ ~@a)))"]
+  ["splice in vector" "[1 2 3 0 1 2 3]" "(let [b [0] a [1 2 3] e []] `[~@e ~@a ~@b ~@a ~@e])"])
+  # gap (jolt-edb): ~/~@ aren't processed inside set literals (`#{~@a} keeps the
+  # unquote-splicing form literal).