fix(generator): dispatch DI projections through partial-class override (marten#4787)

[jeremydmiller]

Fixes the runtime regression introduced by #470 / 2.14.1's GetUninitializedObject shadow-instance fallback. Reported in marten#4787.

Root cause

The 2.14.1 fallback in EvolverCodeEmitter.BuildProjectionInstanceExpression (EvolverCodeEmitter.cs:152-163) closed CS7036 for DI-only-ctor projections at compile time, but the file-scoped Evolver it produced built its private shadow projection via RuntimeHelpers.GetUninitializedObject — bypassing the constructor entirely. Every conventional Apply / Create / ShouldDelete then dispatched through that shadow, so any deref of a constructor-injected field NRE'd. The reporter's null-conditional masked it as silent zero events.

Fix shape

When the projection has at least one instance-on-projection convention method AND no public parameterless ctor AND is partial, emit a [GeneratedCode]-attributed override (Evolve / EvolveAsync / DetermineActionAsync — picked by HasShouldDelete / HasAnyAsync exactly like the existing file-scoped Evolver) directly into the user's partial class. Body uses bare convention-method calls so dispatch binds to this — the DI-built instance with all injected fields populated.

For this path the [assembly: GeneratedEvolver(...)] attribute and the file sealed class Evolver are NOT emitted — the runtime's isOverridden(...) precedence (JasperFxAggregationProjectionBase.cs:82-114) picks up the partial-class override before tryUseAssemblyRegisteredEvolver ever runs, so the file-scoped path is unreachable for this case.

Stateless / parameterless-ctor / aggregate-only / static-only projections keep the file-scoped Evolver verbatim — no perf or shape change for the cases that don't need DI.

Plumbing

• New helpers: HasPublicParameterlessCtor, InstanceCallPrefix, three EmitXAsOverride entry points, EmitPartialProjectionWithDIOverride.
• dispatchOnThis flag threaded through EmitCreateCallSync / EmitCreateCall / EmitApplyCallExpression / EmitApplyCallStatement / EmitShouldDeleteCall and the four Null/NonNull/{Sync,Async} case generators. When true, instance calls emit bare method names (binding to this); when false (default), they emit the existing _projection. prefix for the file-scoped Evolver path — so the existing emission is unchanged for everything except DI projections.

Test

• di_activated_projection_without_parameterless_ctor_compiles → renamed to di_activated_projection_without_parameterless_ctor_dispatches_through_partial_override. Assertion flipped: source must NOT contain GetUninitializedObject / file sealed class / [assembly: GeneratedEvolver] / _projection.Create / _projection.Apply for a DI projection; MUST contain a partial class DiActivated with a [GeneratedCode] override Evolve(...) on it. Compile check (no CS7036) preserved.
• 24/24 AggregateEvolverGeneratorTests green.
• Verified locally against marten#4787 Bug_4787_di_projection_with_instance_apply (9 cases — Apply/Create/ShouldDelete × Singleton/Scoped/Transient): all pass; before this all 9 failed with NRE through the shadow instance.
• Marten regression sweep on net10 against a locally-packed build of this branch: 71/71 ContainerScopedProjectionTests + 1411/1411 EventSourcingTests + 198/198 DaemonTests all green.

Marten consumption

Follow-up Marten PR will bump JasperFx.Events to the version this ships in, promote the repro to the regression suite, and close marten#4787.