Implement event tables

[cloutiertyler]

Description of Changes

Adds event tables support to SpacetimeDB (Rust server bindings only, V10 ABI).

Event tables are write-only tables whose rows persist to the commitlog but are NOT merged into committed state. Their rows are ephemeral in memory — only visible to V2 subscribers in the transaction that inserted them.

Schema & ABI:

• Add is_event: bool to RawTableDefV10, TableDef, and TableSchema
• New st_event_table system table (TableId 17) tracks which tables are event tables, avoiding migration of StTableRow
• is_event is reconstructed from st_event_table in schema_for_table_raw()

Rust bindings macro:

• Add event keyword: #[spacetimedb::table(name = my_events, public, event)]
• Emits const IS_EVENT: bool = true; on TableInternal
• Wired through register_table() to V10 builder's .with_event()

Core behavior:

• merge_apply_inserts(): event table rows are recorded in TxData (for commitlog + subscriptions) but skip merging into committed state
• replay_insert(): event table rows return early — no committed state rebuilt on restart

Compile-time semi-join validation:

• CanBeLookupTable marker trait in query-builder — event tables don't implement it
• Semi-join methods require R: CanBeLookupTable, giving a compile error if an event table is used as the lookup side

Cherry-picks joshua/shub/raw-module-def-v10 (#4153) as a prerequisite. V9 is completely untouched.

Deferred: V2 subscription evaluation, runtime SQL semi-join validation, view validation.

API and ABI breaking changes

New field is_event: bool added to RawTableDefV10 (appended at end for ABI compat). Defaults to false, so existing modules are unaffected.

CanBeLookupTable trait bound replaces HasIxCols on semi-join methods in the query builder. All non-event tables implement CanBeLookupTable, so existing code compiles unchanged.

Expected complexity level and risk

3 — The changes touch the schema pipeline end-to-end (raw def → validated def → runtime schema → system table → committed state merge/replay), but each individual change is straightforward. The main risk area is the merge skip logic in committed_state.rs, which is on the hot path and must correctly distinguish event tables from persistent ones. The system table approach avoids any migration risk for existing databases.

Testing

• cargo check passes (verified locally)
• Verify event table inserts are recorded in TxData for commitlog persistence
• Verify committed state remains empty for event tables after merge
• Verify replay skips event table rows (state stays empty after restart)
• Verify compile error when using event table as right side of query builder semi-join
• Verify non-event tables are completely unaffected