checkIntLiteralFits range-checks a literal against its integer target
(builtins + custom widths via intLiteralRange; width-64 types skip —
every representable literal is a legal bit pattern there) and diagnoses
with the type's range and an xx/cast hint. Wired into the .int_literal
arm (covers decls, assignments, call args, struct-literal fields),
lowerStructConstant, and globalInitValue.
A negated literal now folds to a single constant so -128 range-checks
as -128 rather than as an out-of-range +128 intermediate. An explicit
xx operand skips the check — truncation stays available on request
(cast(T) was already exempt: its value arg lowers without the target).
examples/0300-closures-lambda.sx pinned 133 wrapping to -3 through an
s3 param — the exact class this outlaws; updated to a fitting value.
Found during the fix and filed separately: issue 0113 (negated-literal
global initializers rejected as non-constant; pre-existing).
Regressions: examples/1156-diagnostics-int-literal-out-of-range.sx,
examples/0174-types-int-literal-boundaries.sx.
lowerVarDecl (unannotated) and lowerDestructureDecl now clear target_type
around the initializer lowering: a declaration without annotation provides
no target, so int/float literals take their spec defaults (s64/f64) instead
of the enclosing function's implicit-return type (x := 0 in a -> s8 fn was
s8; big := 3000000000 in -> s32 silently wrapped to -1294967296).
Regression: examples/0173-types-int-literal-default-s64.sx. The remaining
explicit-annotation wrap (x : s8 = 300) is filed as issue 0112.
