rust: replace rustdoc references to alloc::format

Replace alloc::format[1] in the pr_* and dev_* macros' doc comments
with std::format[2] because they are identical but less likely to get
confused with the kernel's alloc crate.

And add a url link for the std::format! macro.

Link: https://doc.rust-lang.org/alloc/macro.format.html [1]
Link: https://doc.rust-lang.org/std/macro.format.html

 [2]
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Andrew Ballance <andrewjballance@gmail.com>
Link: https://lore.kernel.org/r/20250325133352.441425-1-andrewjballance@gmail.com


[ Fixed typo and reworded slightly. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>