Finch 2.4.0: methods, maps, errors as values; str() of any value; macOS and ARM64 docs; Kate support

- fn Struct.method(...) with self by reference, also on C structs
- map[K]V: insertion-ordered hash maps, literals, m[k] += 1, has/get/remove/keys/values
- -> T! / -> !, return error(...), or <value>, or { err }, try; fallible int/float/read_file/write_file/delete_file
- for i, x in list / for k, v in map
- print and str() share one text formatter
- LSP: method and map completion, method signatures; grammar and snippets for VS Code and Kate
- tests: 74 (methods, errors, maps + 11 failure cases); docs at all three levels, en and pl

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/run/geometry.fch

@@ -16,3 +16,8 @@ fn add(Vec a, Vec b) -> Vec {
 fn describe(Vec v) -> str {
     return "(" + str(v.x) + ", " + str(v.y) + ") of length " + str(length(v))
 }
+
+// a method in a module: callable as v.scaled(2) wherever Vec is used
+fn Vec.scaled(float k) -> Vec {
+    return Vec(self.x * k, self.y * k)
+}