feat: replace generic BufferFind with dedicated hasMethod for duplicate detection

Replace the generic `wrenIntBufferFind` function with a specialized `hasMethod` helper that performs exact method symbol matching in the compiler. This change removes the generic `BufferFind` macro from the buffer utility system and introduces a focused implementation in `wren_compiler.c` that directly compares method symbols using `memcmp`. The error message for duplicate methods is also simplified to exclude the module name. Additionally, a new test file `duplicate_methods.wren` is added to verify error handling for duplicate instance and static method definitions.

test/language/method/duplicate_methods.wren

@@ -0,0 +1,11 @@
+class Foo {
+  construct new() {}
+  foo() {}
+  foo() {} // expect error
+  
+  static bar() {}
+  static bar() {} // expect error
+  
+  baz() {}
+  static baz() {}
+}