Move call-result-type discovery out of Lowering into a new src/ir/calls.zig
(CallResolver): the A3.1 Lowering.inferCallType body moves verbatim into
CallResolver.resultType. inferExprType's `.call` arm now delegates via
callResolver(); Lowering.inferCallType is gone.
CallResolver is a *Lowering facade (Principle 5, like ExprTyper/PackResolver):
call typing reads live lexical-scope / target-type state and the function /
foreign-class / protocol resolver helpers, so it borrows *Lowering. Transform
was `self.` -> `self.l.` plus the file-local static `resolveBuiltin(` ->
`Lowering.resolveBuiltin(`.
Widened to pub only what the facade actually consumes: resolveTypeArg,
inferGenericReturnType, resolveFuncByName, getProtocolInfo,
resolveForeignMethodReturnType, the static resolveBuiltin, and Scope.lookupFn.
resolveTypeArg widening is genuinely required here — the `cast` builtin's
result type calls it.
calls.test.zig adds focused tests (builtin/reflection classification, unknown
callee -> unresolved) for the scope-free paths. Barrel-wired in ir.zig.
This is the relocation half of PLAN-ARCH A3.2; call LOWERING (lowerCall) still
owns its own dispatch, and the CallPlan convergence (one plan shared by typing
and lowering, deleting the duplicated qualified/bare/lazy logic) remains.
Behavior-preserving. Gate: zig build, zig build test (incl. new CallResolver
tests), bash tests/run_examples.sh -> 356/0. lower.zig 18598 -> 18413.
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