C# client typed query builder

[rekhoff]

Description of Changes

This PR implements the C# client-side typed query builder, as assigned in #3759.

Key pieces:

• Added a small C# runtime query-builder surface in the client SDK (sdks/csharp/src/QueryBuilder.cs):
  • Query (wraps the generated SQL string)
  • Table<TRow, TCols, TIxCols> (entry point for All() / Where(...))
  • Col<TRow, TValue> and IxCol<TRow, TValue> (typed column references)
  • BoolExpr (typed boolean expression composition)
  • SQL identifier quoting + literal formatting helpers (SqlFormat)
• Extended C# client bindings codegen (crates/codegen/src/csharp.rs) to generate:
  • Per-table/view *Cols and *IxCols helper classes used by the typed query builder.
  • A generated per-module QueryBuilder with a From accessor for each table/view, producing Table<...> values.
  • A generated TypedSubscriptionBuilder which collects Query<TRow>.Sql values and calls the existing subscription API.
  • An AddQuery(Func<QueryBuilder, Query> build) entry point off SubscriptionBuilder, mirroring the proposal’s Rust API.
• Fixed a codegen naming collision found during regression testing:
  • *Cols/*IxCols helpers are now named after the table/view accessor name (PascalCase) instead of the row type, since multiple tables/views can share the same row type (e.g. alias tables / views returning an existing product type).
    C# usage examples (mirroring the proposal’s Rust examples)

1. Typed subscription flow (no raw SQL)

void Subscribe(SpacetimeDB.Types.DbConnection conn)
{
    conn.SubscriptionBuilder()
        .OnApplied(ctx => { /* ... */ })
        .OnError((ctx, err) => { /* ... */ })
        .AddQuery(qb => qb.From.Users().All())
        .AddQuery(qb => qb.From.Players().All())
        .Subscribe();
}

2. Typed WHERE filters and boolean composition

conn.SubscriptionBuilder()
    .OnApplied(ctx => { /* ... */ })
    .OnError((ctx, err) => { /* ... */ })
    .AddQuery(qb =>
        qb.From.Players().Where(p =>
            p.Name.Eq("alice")
                .And(p.IsOnline.Eq(true))
        )
    )
    .Subscribe();

3. “Admin can see all, otherwise only self” (proposal’s “player” view logic, but client-side)

Identity self = /* ... */;

conn.SubscriptionBuilder()
    .AddQuery(qb =>
        qb.From.Players().Where(p =>
            p.Identity.Eq(self)
        )
    )
    .Subscribe();

4. Index-column access for query construction (IxCols)

conn.SubscriptionBuilder()
    .AddQuery(qb =>
        qb.From.Players().Where(
            qb.From.Players().IxCols.Identity.Eq(self)
        )
    )
    .Subscribe();

API and ABI breaking changes

None.

• Additive client SDK runtime types.
• Additive client bindings codegen output.
• No wire-format changes.

Expected complexity level and risk

2 - Low to moderate

• Mostly additive code + codegen.
• The main risk is correctness/compat of generated SQL strings and name/casing conventions across languages; this is mitigated by targeted unit tests + full C# regression test runs.

Testing

• Ran run-regression-tests.sh successfully after regenerating C# bindings.
• Ran C# unit tests using dotnet test sdks/csharp/tests~/tests.csproj -c Release
• Added a new unit test suite (sdks/csharp/tests~/QueryBuilderTests.cs) validating:
  • Identifier quoting / escaping
  • Literal formatting (strings, bools, enums, SpacetimeDB primitive types)
  • NULL semantics for Eq/Neq
  • Boolean expression parenthesization (And/Or/Not)