Add --test mode to elc with Assert stmt and full native test suite passing

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).

lang/el-compiler/runtime/el_runtime.h

@@ -231,6 +231,7 @@ el_val_t  el_html_sanitize(el_val_t input_html, el_val_t allowlist_json);
 el_val_t  fs_read(el_val_t path);
 el_val_t  fs_write(el_val_t path, el_val_t content);
 el_val_t  fs_list(el_val_t path);
+el_val_t  fs_list_json(el_val_t path);
 el_val_t  fs_exists(el_val_t path);
 el_val_t  fs_mkdir(el_val_t path);   /* mkdir -p, mode 0755                */
 
@@ -260,6 +261,9 @@ el_val_t  json_set(el_val_t json_str, el_val_t key, el_val_t value);
 el_val_t  json_array_len(el_val_t json_str);
 el_val_t  json_array_get(el_val_t json_str, el_val_t index);
 el_val_t  json_array_get_string(el_val_t json_str, el_val_t index);
+el_val_t  json_escape_string(el_val_t sv);
+el_val_t  json_build_object(el_val_t kvs);
+el_val_t  json_build_array(el_val_t items);
 
 /* ── Time ────────────────────────────────────────────────────────────────── */
 
@@ -272,6 +276,7 @@ el_val_t  time_to_parts(el_val_t ts);
 el_val_t  time_from_parts(el_val_t secs, el_val_t ns, el_val_t tz);
 el_val_t  time_add(el_val_t ts, el_val_t n, el_val_t unit);
 el_val_t  time_diff(el_val_t ts1, el_val_t ts2, el_val_t unit);
+el_val_t  now_ns(void);
 
 /* ── Instant + Duration: first-class temporal types ──────────────────────────
  * Both types share the el_val_t (int64) slot. Instants are nanoseconds
@@ -428,6 +433,8 @@ el_val_t  state_set(el_val_t key, el_val_t value);
 el_val_t  state_get(el_val_t key);
 el_val_t  state_del(el_val_t key);
 el_val_t  state_keys(void);
+el_val_t  state_has(el_val_t key);
+el_val_t  state_get_or(el_val_t key, el_val_t default_val);
 
 /* ── Float formatting ────────────────────────────────────────────────────── */