`lazyLowerFunction` now saves and nulls `pack_arg_nodes`,
`pack_param_count`, `pack_arg_types`, and `inline_return_target`
before lowering the callee's body, then restores them via defer.
Same shape as the save/restore already in `createComptimeFunction`
(issue-0046 fix). Without this, a lazily lowered regular fn called
from inside a pack-fn mono inherited the outer pack maps, and the
`<pack_name>.len` intercept in `lowerFieldAccess` constant-folded
the callee's same-named param to the outer mono's arity.
`examples/173-pack-bare-args-cross-call.sx` now passes; previously-
green tests untouched. 213/213.
0ede0973f4