Make `MIME::Type` immutable?

[halostatue]

Should MIME::Type objects be (mostly) immutable Data objects?

This would necessitate a serious rethink of how mime-types-data management works (since it currently depends on mutability) — but most of that could be resolved with using map instead of each and using MIME::Type#with.

Certain fields would no longer be assignable, but could be updated as long as they aren't frozen — extensions for example could have methods that add or remove values as long as we don't call extensions#freeze. We would want to #freeze all of the string values, although string interning would handle that for us.

If we do this, it's likely that we would want to be able to replace values in MIME::Types on update, preferably with specific methods for this.

[halostatue]

The recalculation of sort priority by the addition or removal of extensions, however, would no longer be possible with immutable data objects. That's not necessarily a bad thing, but it does change behaviour. Need to consider.