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