feat: support schedule_reinit() under panic=abort builds

[guybedford]

Summary

Previously handler::schedule_reinit() was a no-op under panic=abort. This extends it to work with both panic strategies.

Under panic=abort there's no __instance_terminated flag or wasm-level catch wrappers, so the full abort detection machinery doesn't apply. But schedule_reinit() is independent of abort detection — it just sets a JS-side flag (__wbg_reinit_scheduled) that's checked before each export call. This PR adds that minimal path.

• Remove #[cfg(panic = "unwind")] gate on schedule_reinit() so it calls __wbindgen_reinit() in all builds
• Add generate_reinit_guard() — emits a simple __wbg_termination_guard that only checks __wbg_reinit_scheduled (no try/catch, no __instance_terminated)
• Refactor maybe_wrap_try_catch into maybe_wrap_export_call with separate check_aborted / check_reinit flags — exports under panic=abort get the guard prepended without try/catch wrapping
• Fix __wbg_reset_state to reset __wbg_reinit_scheduled in all builds (not just when wrapped_js_tag is present)
• Add reinit_panic_abort integration test: builds with -Cpanic=abort -Zbuild-std=std,panic_abort, verifies new instance creation, static reset, persistence without signal, and multiple reinit cycles

[hoodmane]

LGTM aside from a few suggestions.