Create Test of C# Code Generation for Tables with BTree indexes of type Identity

[rekhoff]

Action to perform:

Add a test to com.clockworklabs.spacetimedbsdk that checks code generation of a Table with an index of type btree of an Identity type is generating C# code as intended. Manually performed example from https://github.com/clockworklabs/SpacetimeDB/pull/2354 that should be reproduced in an automated test:

1. Created a test project with a Rust server defining a table with a btree index like:

#[index(btree)]
pub identity: Identity,

and another where a table was defined with: #[spacetimedb::table(name = period_timer, scheduled(period, at = scheduled_at), index(name = identity, btree(columns = [identity])))] 2. Published the server. 3. Created a C# client and generated the bindings. 4. Confirmed issue existed prior to change: IDE reports an error in the table definition of The type 'SpacetimeDB.Identity' must be convertible to 'System.IComparable<SpacetimeDB.Identity>' in order to use it as parameter 'Column' in the generic class 'SpacetimeDB.RemoteTableHandle<EventContext,Row>.BTreeIndexBase<Column>' 5. Made change contained in this PR. 6. Rebuilt SpacetimeDB executables, and C# SDK NuGet files. 7. Tested again by republishing and regenerating bindings. 8. Observed IDE no longer reports issue.

Ticket Generated from the comment: https://github.com/clockworklabs/SpacetimeDB/pull/2354#pullrequestreview-2665201801