Add struct instantiation shortcut syntax

[fcoury]

Add support for struct instantiation shortcut syntax.

• Parser Changes:

  • Update parse_struct_init function in src/parser.rs to handle the new shortcut syntax for struct instantiation.
  • Modify parse_struct_init to check if the field name is the same as the variable name and handle accordingly.

• Interpreter Changes:

  • Update evaluate_expr function in src/interpreter.rs to handle the new shortcut syntax for struct instantiation.
  • Modify evaluate_expr to check if the field name is the same as the variable name and handle accordingly.

• Test Updates:

  • Update tests/scripts/struct.hk to use the new shortcut syntax for struct instantiation.
  • Update tests/scripts/impl.hk to use the new shortcut syntax for struct instantiation.

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