feat: ##Inf/##-Inf/##NaN literals, infinite?/NaN?, fix intval? for infinity

The reader now reads the symbolic float values ##Inf, ##-Inf and ##NaN. Added
infinite? and NaN? predicates. Fixed intval? to exclude infinity (floor(inf)=inf
but inf isn't integer-valued), so float?/double? are true for ##Inf and
int?/pos-int?/nat-int?/neg-int? are false for it.

This unblocked many number-test files whose  forms previously failed to
READ (##Inf/##NaN literals), so clojure-test-suite jumped from 2241 to 2539
assertions and pass 1719 -> 1955. Baseline raised to 1900. NaN_qmark now runs.

float?/double? on integer-valued doubles (1.0) remain false: Janet represents
an integer and an integer-valued double identically, so they're inherently
indistinguishable — documented in the README Numbers section.

spec: numbers/floats-&-symbolic-values (15 cases). jpm test green.
Closes jolt-fy8 (fixable parts; int-vs-float ambiguity is a documented divergence).

test/integration/clojure-test-suite-test.janet

@@ -18,7 +18,7 @@
 
 # Baseline: assertions Jolt currently passes across the suite. Raise as Jolt
 # improves so a regression (previously-passing assertion breaking) is caught.
-(def baseline-pass 1650)
+(def baseline-pass 1900)
 # A file is "clean" when it ran with zero failures AND zero errors.
 (def baseline-clean-files 22)
 # Per-file wall-clock budget (seconds). Normal files finish in well under 1s;