Route Parameter Variable Ordering in Marten Batch Queries

[carcer]

This PR fixes a code generation bug where route parameters were used before they were declared when combining [WriteAggregate]/[ReadAggregate] attributes with Load/Before midleware methods.

The fix ensures MartenBatchFrame properly declares its dependencies on variables used by batchable frames, allowing the code generation topological sort to order frames correctly.

Issue

When an endpoint combined:

1. A middleware method like Load(Guid id) or Before(Guid id)
2. A [WriteAggregate] or similar attribute

The generated code would fail with CS0841: Cannot use local variable 'id' before it is declared because:

• The batch query enlistment code tried to use the route parameter id
• But the route parameter variable was declared AFTER the batch query code
• This happened because MartenBatchFrame didn't declare its dependencies on route parameters

Root Cause

The MartenBatchFrame.FindVariables() method only yielded IDocumentSession and CancellationToken, but not the variables that its batchable frames (like LoadAggregateFrame) needed.

Solution

Adjusted MartenBatchFrame.FindVariables() to also enumerate and yield all variables that its enlisted batchable frames depend on.

Test Results

reacting_to_read_aggregate was modified to add Load and Before., this cuased 3 tests to fail. Adding the fix makes them pass, and not additional tests to fail.

Generated Code Verification

The generated code now correctly declares the route parameter before using it in the batch query:

// Before (broken):
var stream_letters_BatchItem = batchedQuery.Events.FetchForWriting<LetterAggregate>(id);  // ERROR: id not declared
await batchedQuery.Execute(httpContext.RequestAborted);
string id_rawValue = (string?)httpContext.GetRouteValue("id");
System.Guid id = default;

// After (correct):
string id_rawValue = (string?)httpContext.GetRouteValue("id");
System.Guid id = default;
var batchedQuery = documentSession.CreateBatchQuery();
var stream_letters_BatchItem = batchedQuery.Events.FetchForWriting<LetterAggregate>(id);  // OK: id declared
await batchedQuery.Execute(httpContext.RequestAborted);