feat: Add module lifecycle reducer

[ritankarsaha]

Description of Changes

Fixes #5480

Adds a stop module lifecycle reducer, the symmetric counterpart to init, invoked exactly once immediately before a database is permanently destroyed via spacetime delete or a reset. It does not fire on an ordinary module update/hot-reload or on replica scale-down, since the database's data survives both, and it's best-effort: a failing, trapping, or slowstop reducer is logged but never blocks the deletion it precedes.

Implemented via #[reducer(stop)] (Rust), ReducerKind.Stop (C#), and spacetime.stop() (TypeScript). Core changes: new Lifecycle::Stop variant, ModuleHost::call_module_stop (wired through both the WASM and V8/JS instance paths), and a new is_final_teardown flag on HostController::exit_module_host, set only by the standalone control plane's delete_database/reset_database paths (not replica scale-down/decommission).

Adds a module-test-stop fixture module and an integration test verifying stop fires exactly once on deletion and not on update.

API and ABI breaking changes

None. This is a purely additive change: a new Lifecycle enum variant and a new reducer-kind/attribute surface in each binding. No existing behavior changes for modules that don't declare a stop reducer.

Expected complexity level and risk

2.5 - touches the module lifecycle/shutdown path in crates/core/src/host The main risk surface is the is_final_teardown threading through crates/standalone/src/lib.rs's four delete_replica call sites — getting one of those wrong could either misfire stop on routine replica scale-down or silently skip it on real deletion.

Testing

• cargo test -p spacetimedb-schema — new duplicate-lifecycle tests for Stop (v9 + v10)
• cargo fmt --check and cargo clippy -D warnings clean on spacetimedb-lib, spacetimedb-schema, spacetimedb-core, spacetimedb-standalone, spacetimedb-bindings-macro, spacetimedb, spacetimedb-testing
• New integration test test_stop_reducer_fires_only_on_deletion against a real compiled module, confirming stop does not fire on update and fires exactly once on deletion
• TypeScript: tsc --noEmit, eslint, and prettier --check all clean; full vitest suite (232/232) passes
• Manual: publish a module with stop, confirm no fire across spacetime publish, exactly one fire on spacetime delete, and rejection on a direct spacetime call <module> stop

[bfops]

Hi @ritankarsaha, what's the motivation for adding this reducer?

[ritankarsaha]

Hi @ritankarsaha, what's the motivation for adding this reducer?

This is in context to an issue #5480 which mentions for a similar reducer during teardown.

[ritankarsaha]

Hi @ritankarsaha, what's the motivation for adding this reducer?

Could you point me to more issues requiring attention?
I would like to contribute to the project more.

Do you guys have any community meet? @bfops