feat(stdlib): add String_Chars, String_FromBool, fix Fmt and Net

- String.bux: add String_Chars(s, index) for char-at-index access
- String.bux: add String_FromBool(b) conversion
- Fmt.bux: rewrite with correct stdlib imports (was using non-existent names)
- Net.bux: fix String_Len -> bux_strlen (String_Len not imported)
- All lib modules compile successfully

lib/Fmt.bux

@@ -1,42 +1,100 @@
+// Fmt.bux — String formatting with positional placeholders {0}, {1}, {2}...
+//
+// Usage:
+//   Fmt_Fmt1("Hello, {0}!", "World")
+//   Fmt_FmtInt("Count: {0}", 42)
+//   Fmt_FmtBool("Active: {0}", true)
+//   Fmt_Fmt2("Name: {0}, Age: {1}", name, String_FromInt(age))
+
 module Std::Fmt {
-/* String formatting with positional placeholders {0}, {1}, {2}...
- *
- * Usage:
- *   Fmt_Fmt1("Hello, {0}!", "World")
- *   Fmt_FmtInt("Count: {0}", 42)
- *   Fmt_FmtFloat("Pi: {0}", 3.14159)
- *   Fmt_FmtBool("Active: {0}", true)
- *   Fmt_Fmt2("Name: {0}, Age: {1}", name, String_FromInt(age))
- */
 
-func Fmt_Fmt1(pattern: String, a: String) -> String {
-    return String_Format1(pattern, a);
-}
+import Std::String::{
+    String_Eq,
+    String_FromInt,
+    String_FromFloat,
+    String_FromBool,
+    StringBuilder,
+    StringBuilder_New,
+    StringBuilder_Append,
+    StringBuilder_Build,
+    String_Chars
+};
 
-func Fmt_Fmt2(pattern: String, a: String, b: String) -> String {
-    return String_Format2(pattern, a, b);
-}
+extern func bux_strlen(s: String) -> uint;
+extern func bux_str_to_int(s: String) -> int64;
+extern func bux_alloc(size: uint) -> *void;
 
-func Fmt_Fmt3(pattern: String, a: String, b: String, c: String) -> String {
-    return String_Format3(pattern, a, b, c);
-}
-
-func Fmt_FmtInt(pattern: String, n: int64) -> String {
-    return String_Format1(pattern, String_FromInt(n));
-}
-
-func Fmt_FmtInt2(pattern: String, n1: int64, n2: int64) -> String {
-    return String_Format2(pattern, String_FromInt(n1), String_FromInt(n2));
-}
-
-func Fmt_FmtFloat(pattern: String, f: float64) -> String {
-    return String_Format1(pattern, String_FromFloat(f));
-}
-
-func Fmt_FmtBool(pattern: String, b: bool) -> String {
-    if b {
-        return String_Format1(pattern, "true");
+// Core formatting engine: replace {0}..{9} in template with args
+func Fmt_Format(tmpl: String, argStrs: *String, argCount: int) -> String {
+    let sb: StringBuilder = StringBuilder_New();
+    var i: uint = 0;
+    let tmplLen: uint = bux_strlen(tmpl);
+    while i < tmplLen {
+        // Check for {
+        let ch: String = String_Chars(tmpl, i);
+        if String_Eq(ch, "{") {
+            let digitIdx: uint = i + 1;
+            if digitIdx < tmplLen {
+                let digitCh: String = String_Chars(tmpl, digitIdx);
+                let d: int64 = bux_str_to_int(digitCh);
+                if d >= 0 && d < argCount as int64 {
+                    // Consume {d}
+                    i = i + 2; // skip past digit
+                    // Check for closing }
+                    if i < tmplLen {
+                        let closeCh: String = String_Chars(tmpl, i);
+                        if String_Eq(closeCh, "}") {
+                            i = i + 1; // skip }
+                            let argStr: String = *(argStrs + (d * 8) as uint);
+                            StringBuilder_Append(&sb, argStr);
+                            continue;
+                        }
+                    }
+                }
+            }
+        }
+        // Normal character: append it
+        StringBuilder_Append(&sb, ch);
+        i = i + 1;
     }
-    return String_Format1(pattern, "false");
+    return StringBuilder_Build(&sb);
 }
+
+// Convenience wrappers
+func Fmt_Fmt1(tmpl: String, a1: String) -> String {
+    var args: *String = bux_alloc(8) as *String;
+    *(args + 0) = a1;
+    return Fmt_Format(tmpl, args, 1);
+}
+
+func Fmt_FmtInt(tmpl: String, val: int64) -> String {
+    let s: String = String_FromInt(val);
+    return Fmt_Fmt1(tmpl, s);
+}
+
+func Fmt_FmtBool(tmpl: String, val: bool) -> String {
+    let s: String = String_FromBool(val);
+    return Fmt_Fmt1(tmpl, s);
+}
+
+func Fmt_FmtFloat(tmpl: String, val: float64) -> String {
+    let s: String = String_FromFloat(val);
+    return Fmt_Fmt1(tmpl, s);
+}
+
+func Fmt_Fmt2(tmpl: String, a1: String, a2: String) -> String {
+    var args: *String = bux_alloc(16) as *String;
+    *(args + 0) = a1;
+    *(args + 8) = a2;
+    return Fmt_Format(tmpl, args, 2);
+}
+
+func Fmt_Fmt3(tmpl: String, a1: String, a2: String, a3: String) -> String {
+    var args: *String = bux_alloc(24) as *String;
+    *(args + 0) = a1;
+    *(args + 8) = a2;
+    *(args + 16) = a3;
+    return Fmt_Format(tmpl, args, 3);
+}
+
 }