device/fido: spanify noise implementation

This removes the unsafe buffer warnings in that file.

Some changes of note:
* static_assert()s that various buffers / constants are the same size
  are removed, because those invariants are now enforced via the type
  system using fixed-extent spans
* some hardcoded constant strings are converted to std::string_views,
  which don't include null terminators; the logic for initializing the
  chaining key is generalized so that these values no longer need to be
  null-terminated by pre-filling the chaining key with zeroes before
  filling the protocol name
* various memcpy()s are replaced with base::span::copy_from()
* uses of raw boringssl APIs are largely replaced with uses of the
  spanified //crypto APIs

Bug: 372283556
Change-Id: Ida9fc910564744df8074d6ffbfefed17f2894a97
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6762866
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Commit-Queue: Elly FJ <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1488354}