Implements IComparable for Identity and ConnectionId

[rekhoff]

Description of Changes

Implements IComparable for Identity and ConnectionId

This relates to the following issue:
#2348

API and ABI breaking changes

Not a breaking change. Adds functionality and fixes bug.

Expected complexity level and risk

1

Testing

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.

• Tested IDE no longer reports error after change.

[kazimuth]

Could you add a basic test to BSATN.Runtime.Tests for these? With that I'm happy with this.

It would be nice to add a test to the SDK as well duplicating what you said you did in the PR description, but unfortunately that would require a PR in a different repo...

[rekhoff]

BSATN.Runtime.Tests added for both Identity and ConnectionId.
Marking as ready for merge.
This PR will resolve issue: #2348
New issue created for adding a test that performs the manually performed actions outlined in the description of this PR:
#2362