datastore: add support for truncation

[Centril]

Description of Changes

Adds support for truncation in the datastore.
The commitlog format already supported it.
A table is considered truncated in a transaction when there are deletes and when the row count post-deletes is 0.

API and ABI breaking changes

None

Expected complexity level and risk

3?

Testing

Some existing datastore tests have been amended to check whether TxData contain truncation or not.

[Shubham8287]

If you need to reproduce the bug mentioned in comment, I can help but reasoning seems straight-forward.

[Shubham8287]

I am also getting this error while trying to replay from commitlog after module update.

2025-09-17T09:22:34.516339Z ERROR try_init: crates/core/src/host/module_host.rs:396: failed to create table message

Caused by:
    0: DatastoreError: IndexError: Unique constraint violation 'st_table_table_name_idx_btree' in table 'st_table': column(s): '["table_name"]' value: "message"
    1: IndexError: Unique constraint violation 'st_table_table_name_idx_btree' in table 'st_table': column(s): '["table_name"]' value: "message"
    2: Unique constraint violation 'st_table_table_name_idx_btree' in table 'st_table': column(s): '["table_name"]' value: "message"    

With following repo steps:

1. publish quickstart module
2. Make any change in module to change its ModuleDef, ex- remove or add a reducer.
3. republish module and restart the server.
4. make a sql call to actually load the module after restart.

Not reproducible in master, I also tried with rebasing the PR on master.

[Shubham8287]

Merged https://github.com/clockworklabs/SpacetimeDB/pull/3261/files which fixes the previously mentiond issues.