fix(#4966): natural key extractor handles a two-arg static evolve method

[jeremydmiller]

Problem

A natural key that changes via an update event goes unrecorded. Given a self-aggregating aggregate whose [NaturalKeySource] methods are:

[NaturalKeySource] public static Product Create(ProductRegistered e) => new() { Code = new(e.ProductCode) };
[NaturalKeySource] public static Product Apply(ProductCodeChanged e, Product current) => current with { Code = new(e.NewProductCode) };

the two-arg Apply evolve method was silently skipped during natural-key discovery, so no NaturalKeyEventMapping was built for ProductCodeChanged. The mt_natural_key_X lookup table only ever recorded the create event's key and never the changed key — on live inline append or rebuild — leaving FetchLatest-by-natural-key unable to find the stream under its new key.

Reported against a projection rebuild in marten#4966.

Root cause

buildExtractor's static-factory branch matched any static method on the aggregate returning the aggregate type, but composed a one-argument Expression.Call. A two-arg evolve method threw ArgumentException while building the call, which the surrounding catch { /* silently skip */ } swallowed.

Fix

The static-on-aggregate branch now builds one argument per parameter:

• the event parameter receives the raw event data (converted),
• a TDoc parameter (the prior aggregate) receives a fresh default aggregate — mirroring the existing instance-method branch.

Parameters that can't be satisfied from event data alone (IEvent<T> metadata, or a doc type with no public parameterless ctor) fall through to the existing property-matching path, so no previously working shape regresses. All 91 EventTests projection tests pass.

Verification

• New NaturalKeySourceDiscoveryTests.discovers_natural_key_source_on_static_evolve_method_that_changes_the_key.
• Proven end-to-end against Marten with a local package: the marten#4966 repro fails on 2.28.0 ("should not be null but was") and passes with this fix.

Ships as 2.28.1. The superseding Marten PR (retaining the original repro author) bumps to it and closes marten#4966.

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