Refactor `finishBlock` in `wren_compiler.c` to detect single-expression bodies (no newline after `{`) and leave a value on the stack, enabling implicit returns for methods and functions. Add `finishBody` wrapper to handle constructor flag. Update all benchmark and test `.wren` files to remove explicit `return` keywords from getters and single-expression methods, relying on the new implicit return behavior. Remove old `return_null_if_brace.wren` test, add `newline_body.wren`, `newline_in_expression_block.wren`, and `no_newline_before_close.wren` tests for edge cases.
Add support for setter methods in the compiler by detecting '=' after a method name in namedCall, compiling the assigned value, and emitting the setter instruction. Includes new test cases for instance setters, static setters, assignment associativity, grouping, operator precedence errors, setter result values, and same-name getter/setter methods. Also updates the super call test with a TODO for super setter calls.
