JIT: add named-let loops, let/let*, and/or, car/cdr/cons, 18 new tests
JIT now covers: if, cond, and, or, let, let*, named-let (native loops),
car, cdr, cons, null?, pair?, arithmetic, comparisons, recursion, TCO.
1309 lines of x86_64 codegen. 76 C tests + 114 functional tests pass.
Named-let loops compile to native jmp (zero call overhead):
sum-to(50k): 0.33ms JIT vs 7.8ms CPython (24x faster than Python)
ack(3,4): 0.20ms JIT vs 2.0ms CPython (10x faster)
fib-rec(20): 0.42ms JIT vs 2.7ms CPython (6x faster)
EML benchmark added: integer-domain exp/ln composition under JIT.