Allow Long scalar coercion from integer literals during AST input validation

[Copilot]

Inline integer literals for LongType were being rejected in AST validation, even though runtime coercion supports Long. This caused valid mutations/input objects using Long fields (e.g. addressId: 1) to fail before execution.

• Validation logic

  • Updated scalar matching for IntValue in Validation.fs to include Long alongside ID, Int, and Float.
  • This aligns AST literal validation with existing scalar coercion behavior.

• Regression coverage

  • Extended AstValidationTests schema fixture with a longArgField(longArg: Long) argument path.
  • Added a passing validation case for integer-to-long coercion via inline literal.

| IntValue _ ->
    match tref.Name, tref.Kind with
    | Some ("ID" | "Int" | "Long" | "Float"), TypeKind.SCALAR -> Success
    | _ -> canNotCoerce