rust: transmute: add `from_bytes_copy` method to `FromBytes` trait

rust: transmute: add `from_bytes_copy` method to `FromBytes` trait

`FromBytes::from_bytes` comes with a few practical limitations:

- It requires the bytes slice to have the same alignment as the returned
  type, which might not be guaranteed in the case of a byte stream,
- It returns a reference, requiring the returned type to implement
  `Clone` if one wants to keep the value for longer than the lifetime of
  the slice.

To overcome these when needed, add a `from_bytes_copy` with a default
implementation in the trait. `from_bytes_copy` returns an owned value
that is populated using an unaligned read, removing the lifetime
constraint and making it usable even on non-aligned byte slices.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Link: https://lore.kernel.org/r/20250826-nova_firmware-v2-1-93566252fe3a@nvidia.com
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>