An `xx <int>` argument to a variadic `format`/`print` (a comptime `..$args`
pack) segfaulted when the call was inside an imported-module function. Root
cause: lowerPackCall lowered each pack arg with whatever self.target_type was
set to from the surrounding context. A bare arg is unaffected (inferExprType
ignores target_type), but `xx <expr>`'s result type IS target_type — so
`format("…", xx i)` inside a `-> string` fn cast the int to `string`,
monomorphized __pack_string, and ABI-coerced the 4-byte int as a 16-byte string
fat pointer → corruption. Inline it worked only because target_type was null
there; the imported-module path left it set.
Fix: save/clear/restore self.target_type around the pack-arg lowering loop. A
pack arg is independently typed — comptime `..$args` auto-boxes to Any; a value
pack takes its declared element/protocol type — never a leftover outer target.
examples/242-xx-any-pack-cross-module.sx (+ companion fmt.sx) is the regression.
issues/0057 marked resolved. Unblocks ERR E3.3 (the trace.sx formatter formats
frames with `xx frame`).
Gates: zig build, zig build test, bash tests/run_examples.sh (279 passed; lone
failure is the user's uncommitted 213-canonical-map pack WIP).
