module: zero-init `export_set_changed_since_require_world` on module creation (#61874)

fix is fully claude one shot. I was also able to glean a small
reproducible test, but it was not deterministic and I don't have
confidence it would work on all machines, so I omitted it.


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This `_Atomic(int8_t)` field was added in #57421 but never initialized
in `jl_new_module__`. `jl_gc_alloc` does not zero the returned memory,
so each fresh module started with whatever garbage was in the pool slot.
The field is read by `all_usings_unchanged_implicit` in
`src/staticdata.c` during pkgimage loading: a non-zero garbage value
spuriously forces binding-partition revalidation for downstream modules.

The fix matches the existing zero-init of the adjacent `has_reexports`
field that was added in #59859.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>