Make page CRC verification toggleable by end-users

[AlexTMjugador]

These changes make the Ogg page CRC verification check toggleable at runtime by end-users via a new PageParsingOptions struct that may be passed at reader/parser construction time. I have paid special attention to making the new feature both backwards and forwards compatible, which led me to taking the following design choices:

• No signature of any existing public method was modified. People looking into changing parsing behavior via the new PageParsingOptions struct must use the new *_with_parse_opts methods.
• Marking PageParsingOptions as #[non_exhaustive], so that we may add new public fields to it in the future without a semver-breaking change. Users must always default-initialize this struct. It only derives Clone too, in case we ever need to make it hold non-Copy types.
• Shared ownership of the PageParsingOptions between different reader structs is achieved through Arcs, which ensures that no struct stops being Send or Sync with a negligble performance impact.

The fuzzing cfg flag is still honored after these changes by using it to set a default value for the new verify_checksum page parsing option accordingly.

The need for these changes has been brought forward in https://github.com/OptiVorbis/OptiVorbis/issues/101.

[AlexTMjugador]

This PR also bumps the MSRV to 1.61 to fix CI checks, as it is required for the current code to work anyway (the screenshot below is from cargo msrv):

[AlexTMjugador]

Thanks for the quick review and merge! :rocket:

I was wondering if there are any plans to publish a release with these changes soon? I'd love to try them out on a new OptiVorbis release too, but no worries if we have to wait a little longer 😉