js-on-sx: NaN / Infinity resolve at transpile; strict-eq returns false for NaN

Previously NaN / Infinity were SX symbols that couldn't be (define)'d
because the SX tokenizer parses 'NaN' and 'Infinity' as numeric literals.

js-transpile-ident now rewrites NaN -> (js-nan-value), Infinity ->
(js-infinity-value), each a zero-arg function returning the appropriate
IEEE value ((/ 0.0 0.0) and (/ 1.0 0.0)).

Also fixes js-number-is-nan: in this SX, (= nan nan) returns true, so the
classic 'v !== v' trick doesn't work. Now checks (inspect v) against
'nan'/'-nan' strings.

Extends js-strict-eq: NaN === NaN returns false per ES spec.

8 new unit tests, 497/499 total.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/js/transpile.sx

@@ -157,6 +157,8 @@
     (name)
     (cond
       ((= name "undefined") (list (js-sym "quote") :js-undefined))
+      ((= name "NaN") (list (js-sym "js-nan-value")))
+      ((= name "Infinity") (list (js-sym "js-infinity-value")))
       (else (js-sym name)))))
 
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