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/fail/error_not_fallible.fch

@@ -0,0 +1,9 @@
+// expect: 'check' can't fail, so it can't return an error (make it fallible: -> !)
+fn check(int n) {
+    if n < 0 {
+        return error("negative")
+    }
+}
+fn main() {
+    check(1)
+}

tests/fail/error_outside_return.fch

@@ -0,0 +1,4 @@
+// expect: error(...) makes an error to return from a function that can fail
+fn main() {
+    e := error("oops")
+}

tests/fail/map_empty_literal.fch

@@ -0,0 +1,4 @@
+// expect: an empty [:] needs a type, like: map[str]int m = [:]
+fn main() {
+    m := [:]
+}

tests/fail/map_float_key.fch

@@ -0,0 +1,5 @@
+// expect: a map key must be a whole number, a char, a bool or a str, not float
+fn main() {
+    map[float]int m
+    print(m)
+}

tests/fail/map_missing_key.fch

@@ -0,0 +1,5 @@
+// expect: the key "zoe" is not in the map
+fn main() {
+    ages := ["anna": 31]
+    print(ages["zoe"])
+}

tests/fail/method_field_clash.fch

@@ -0,0 +1,9 @@
+// expect: the struct Point already has a field named 'x'
+struct Point {
+    int x
+}
+fn Point.x() -> int {
+    return 1
+}
+fn main() {
+}

tests/fail/method_loop_readonly.fch

@@ -0,0 +1,12 @@
+// expect: the loop variable 'c' can't be changed
+struct Counter {
+    int n
+}
+fn Counter.bump() {
+    self.n += 1
+}
+fn main() {
+    for c in [Counter(1), Counter(2)] {
+        c.bump()
+    }
+}

tests/fail/method_missing.fch

@@ -0,0 +1,8 @@
+// expect: the struct Point has no methods; add one with  fn Point.norm(...) { ... }
+struct Point {
+    int x
+}
+fn main() {
+    p := Point(1)
+    print(p.norm())
+}

tests/fail/or_block_value.fch

@@ -0,0 +1,5 @@
+// expect: this block must leave with return, break, continue or exit
+fn main() {
+    n := int("x") or { print("not a number") }
+    print(n)
+}

tests/fail/or_cannot_fail.fch

@@ -0,0 +1,4 @@
+// expect: this call can't fail, so it needs no 'or' or 'try'
+fn main() {
+    print(int(3.5) or 0)
+}

tests/fail/try_outside_fallible.fch

@@ -0,0 +1,10 @@
+// expect: try passes the error on, so 'twice' must be able to fail too (-> int!)
+fn parse(str s) -> int! {
+    return int(s) or { return error("bad") }
+}
+fn twice(str s) -> int {
+    return try parse(s) * 2
+}
+fn main() {
+    print(twice("2"))
+}

tests/fail/unhandled_error.fch

@@ -0,0 +1,7 @@
+// expect: 'parse' can fail, so say what happens then
+fn parse(str s) -> int! {
+    return int(s) or { return error("bad") }
+}
+fn main() {
+    print(parse("1"))
+}