fix: allow closed expressions as arguments

[Seddryck]

Summary

• allow closed-expression pipelines directly inside positional arguments
• preserve nested pipelines as the existing closed_expression CST node
• bind nested closed expressions to ClosedExpressionSyntax
• add valid composition, source-order, span, and malformed-input coverage
• update affected invalid parameterized-expression recovery snapshots

This enables expressions such as:

append(.firstName | Titlecase)

Close #45.

Validation

• npx tree-sitter test — 111/111 corpus cases passed
• dotnet test bindings/csharp/Expressif.Syntax.Tests/Expressif.Syntax.Tests.csproj --nologo — 56/56 passed on each of .NET 8, .NET 9, and .NET 10

Environment note

The Node binding smoke test could not run because the local Node 24 native-addon rebuild fails on an existing Windows Release|Win32 project-configuration mismatch. This is unrelated to the grammar change.

[coderabbitai]

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⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: b20205e6-2541-445d-94d5-1103116a1014

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