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/Mem.bux

@@ -0,0 +1,29 @@
+module Std::Mem {
+
+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_mem_eq(a: *void, b: *void, size: uint) -> int;
+
+func Alloc(size: uint) -> *void {
+    return bux_alloc(size);
+}
+
+func Realloc(ptr: *void, size: uint) -> *void {
+    return bux_realloc(ptr, size);
+}
+
+func Free(ptr: *void) {
+    bux_free(ptr);
+}
+
+func MemEq(a: *void, b: *void, size: uint) -> bool {
+    return bux_mem_eq(a, b, size) != 0;
+}
+
+func New<T>() -> *T {
+    let sz: uint = sizeof(T);
+    return bux_alloc(sz) as *T;
+}
+
+}