A literal integer switch over a number tested min <= x <= max with two
ordered compares before converting and round-tripping the discriminant.
The round trip alone already rejects every non-matching value once the
conversion is frozen: NaN and infinities compare unordered, a frozen
out-of-range conversion converts back to a different value, fractions
fail, and -0 selects case 0 like strict equality. Cases in [2^31, 2^32)
dispatch on i64 instead of fptoui to i32.
A discriminant already proven to be an exact integer (int32 slots,
x | 0, x >>> 0, counted-loop counters) now selects directly, narrowing
to i32 only when its proven range fits.
tsc-ts (callgrind, single-threaded): self-check about -0.8 % instructions,
mostly switch (node.kind) and token dispatch.
