Keep LinqraftMapping capture support and remove AsLeftJoin / QueryExtensions work

[Copilot]

This PR narrows the scope back to LinqraftMapping capture variables only. All AsLeftJoin / Linqraft.QueryExtensions work has been removed so it can proceed separately, while mapping-generated methods continue to support captured values.

• Scope reset

  • Removed all AsLeftJoin-related generator changes
  • Removed Linqraft.QueryExtensions package and its registration infrastructure
  • Removed SG / EF Core test coverage that existed only for the left-join extension path
  • Dropped the plan.md content that had shifted to the separate query-extension design

• Mapping capture support retained

  • Kept capture-aware method generation for LinqraftMappingGenerate
  • Kept capture-aware method generation for LinqraftMappingDeclare<T>
  • Generated mapping methods still surface captured values as explicit parameters

• Documentation

  • Expanded docs/library/mapping-methods.md with capture-parameter guidance and examples for both:
    • helper-class mappings
    • static partial class mappings

Example of the retained mapping capture flow:

[LinqraftMappingGenerate("ProjectToDtoWithCapture")]
internal static IQueryable<OrderDto> Template(
    this IQueryable<Order> source,
    int offset,
    string suffix) =>
    source.SelectExpr<Order, OrderDto>(
        order => new
        {
            order.Id,
            AdjustedTotal = order.Total + offset,
            DisplayName = order.Name + suffix,
        },
        capture: () => (offset, suffix)
    );

This keeps the PR focused on the mapping capture feature and leaves the query-extension / left-join work for a separate follow-up.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Use capture member names in generated mapping signatures

The generated mapping method now declares capture parameters using capture.LocalName, which is the internal synthetic name (for example __linqraft_capture_0_offset) rather than the user-facing capture name (offset, suffix). This makes named-argument calls fail (ProjectTo...(..., offset: 10, suffix: "x") no longer compiles) and exposes unstable implementation-detail names in the public API surface, which is especially problematic for mappings generated as public methods.

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[arika0093]

@copilot apply this review

[arika0093]

@copilot apply codex's review.

in src/Linqraft.SourceGenerator/SourceWriters.cs

The generated mapping method now declares capture parameters using capture.LocalName, which is the internal synthetic name (for example __linqraft_capture_0_offset) rather than the user-facing capture name (offset, suffix). This makes named-argument calls fail (ProjectTo...(..., offset: 10, suffix: "x") no longer compiles) and exposes unstable implementation-detail names in the public API surface, which is especially problematic for mappings generated as public methods.

[Copilot]

@copilot apply codex's review.

in src/Linqraft.SourceGenerator/SourceWriters.cs
...

Fixed in d75e27d. The generated mapping signature now uses the stable capture property names (offset, suffix) again, and the generator aliases those parameters back to the existing internal synthetic locals inside the method body so the projection emission still works. I also added a regression test that calls the generated mapping with named arguments.