rust: str: add radix prefixed integer parsing functions

rust: str: add radix prefixed integer parsing functions

Add the trait `ParseInt` for parsing string representations of integers
where the string representations are optionally prefixed by a radix
specifier. Implement the trait for the primitive integer types.

Suggested-by: Benno Lossin <benno.lossin@proton.me>
Tested-by: Daniel Gomez <da.gomez@samsung.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
Signed-off-by: Daniel Gomez <da.gomez@kernel.org>