Add AWSLambda0145 diagnostic for unregistered durable envelope types

[GarrettBeatty]

Description

Adds a new build-time diagnostic AWSLambda0145 (Warning) to the Annotations source generator.

Motivation

With the Annotations model, a [DurableExecution] function's generated handler has the signature:

Task<DurableExecutionInvocationOutput> Handler(DurableExecutionInvocationInput input, ILambdaContext context)

Users never see DurableExecutionInvocationInput / DurableExecutionInvocationOutput in their own code — the generator introduces them. If the function registers the source-generator serializer (SourceGeneratorLambdaJsonSerializer<TContext>), the durable runtime (de)serializes that envelope through the user's JsonSerializerContext. Unlike the reflection-based DefaultLambdaJsonSerializer, a source-gen context only handles types explicitly registered via [JsonSerializable]. If the envelope types aren't registered, the function fails at invocation time with no build-time signal.

This diagnostic surfaces the problem at build time, consistent with the other durable diagnostics (AWSLambda0142–0144).

Behavior

Emitted (Warning) only when all hold:

• the method has [DurableExecution], and
• the registered serializer (method-level attribute, else assembly-level) is SourceGeneratorLambdaJsonSerializer<TContext>, and
• TContext (walking its base contexts) does not register a given envelope type via [JsonSerializable(typeof(...))].

One warning per missing envelope type. Silent for DefaultLambdaJsonSerializer / any non-source-gen serializer, and skipped if the durable types can't be resolved (package not referenced — other diagnostics cover that).

Changes

• TypeFullNames.cs: add SourceGeneratorLambdaJsonSerializer1andJsonSerializableAttribute` constants.
• DiagnosticDescriptors.cs: add DurableExecutionMissingSerializableEnvelope (AWSLambda0145, Warning).
• AnalyzerReleases.Unshipped.md: register the new rule.
• LambdaFunctionValidator.cs: add ValidateDurableExecutionSerializerContext, called from ValidateDurableExecution.
• Tests: DurableExecutionSerializerContextDiagnosticsTests — both registered (no diagnostic), one missing, both missing, and DefaultLambdaJsonSerializer (no diagnostic).
• Added AutoVer changefile (Amazon.Lambda.Annotations, Minor).

Testing

• dotnet build -c Release on the generator: clean.
• All 50 DurableExecution* generator tests pass (net10.0), including the 4 new ones.