Implement compile_test() entry point that emits a C test harness instead
of a normal program. Test blocks (previously skipped) now compile to
static functions with per-assertion pass/fail tracking. Assert statement
added to parser and codegen. Runtime extended with now_ns, fs_list_json,
json_build_object, json_build_array, json_escape_string, state_has,
state_get_or. Fix float negation codegen, float equality comparisons,
time_to_parts return type (JSON string), time_format empty-fmt, json_set
raw-value semantics, state_keys JSON array return. All 310 native tests
pass across 9 suites (core, text, string, math, env, state, json, time, fs).
Combines two orthogonal optimizations:
1. Flat token list (from beta): lex() returns [Any] with alternating kind/value
pairs instead of [Map], eliminating one ElMap per token (~3 mallocs each).
Parser updated: tok_kind(t,i) = t[2*i], tok_value(t,i) = t[2*i+1].
2. Char code dispatch (from alpha): lex() hot loop uses str_char_code -> Int
instead of str_char_at -> strdup String for all character classification.
Eliminates ~400K x 16B = 6.4MB of temporary string allocations.
scan_digits and scan_ident also updated to use str_char_code.
Result on main.el: 17.1MB -> 14.4MB peak RSS (-16%).
Self-hosting: PASS.
Will Anderson