feat(fs): add file stat functionality across platforms

[oboard]

Implement stat functionality to retrieve file metadata including size, timestamps, and permissions. Added native, wasm and JS implementations with tests. The Stats struct contains comprehensive file system information.

Add cross-platform support for stat details with proper handling of platform-specific fields. Includes tests to verify basic functionality and metadata correctness.

///|
pub struct Stats {
  dev : UInt64
  mode : UInt
  nlink : UInt64
  ino : UInt64
  uid : UInt
  gid : UInt
  rdev : UInt64
  atime_sec : Int64
  atime_nsec : Int64
  mtime_sec : Int64
  mtime_nsec : Int64
  ctime_sec : Int64
  ctime_nsec : Int64
  birthtime_sec : Int64
  birthtime_nsec : Int64
  size : Int64
  blocks : UInt64
  blksize : UInt
  flags : UInt
  gen : UInt
  lspare : Int
  qspare : (Int64, Int64)
} derive(Show, Eq)

[peter-jerry-ye]

For the Wasm backend, it would be necessary to update the moonrun as well. See #201 as an example.