feat: restructure repo, borrow checker, expanded stdlib

- Reorganize repository to Rust-style layout:
  compiler/bootstrap/  compiler/selfhost/  compiler/tests/
  library/std/  library/runtime/  tests/  tools/
- Add buxs/ Windows-compatible project root
- Add borrow checker tests and implement:
  - Alias analysis (double mutable borrow detection)
  - Use-after-move detection for own T
- Expand standard library:
  - Std::Os: Args, Env, Cwd, Chdir
  - Std::Time: NowMs, NowUs, SleepMs
  - Std::Process: Run, Output
  - Std::Io: PrintInt64 (fixes 32-bit truncation bug)
- Add examples: os_time.bux, process.bux
- Fix PrintInt to use int64_t in C runtime

library/std/Array.bux

@@ -0,0 +1,44 @@
+module Std::Array {
+
+extern func bux_alloc(size: uint) -> *void;
+extern func bux_realloc(ptr: *void, size: uint) -> *void;
+extern func bux_free(ptr: *void);
+extern func bux_bounds_check(index: uint, len: uint);
+
+struct Array<T> {
+    data: *T,
+    len: uint,
+    cap: uint,
+}
+
+func Array_New<T>(cap: uint) -> Array<T> {
+    let data = bux_alloc(cap * sizeof(T)) as *T;
+    return Array<T> { data: data, len: 0, cap: cap };
+}
+
+func Array_Push<T>(self: *Array<T>, value: T) {
+    if self.len >= self.cap {
+        self.cap = self.cap * 2;
+        self.data = bux_realloc(self.data as *void, self.cap * sizeof(T)) as *T;
+    }
+    self.data[self.len] = value;
+    self.len = self.len + 1;
+}
+
+func Array_Get<T>(self: *Array<T>, index: uint) -> T {
+    bux_bounds_check(index, self.len);
+    return self.data[index];
+}
+
+func Array_Len<T>(self: *Array<T>) -> uint {
+    return self.len;
+}
+
+func Array_Free<T>(self: *Array<T>) {
+    bux_free(self.data as *void);
+    self.data = null as *T;
+    self.len = 0;
+    self.cap = 0;
+}
+
+}