feat: impl ReaderBuilder

[ok-nick]

Implements a ReaderBuilder for constructing a Reader with settings and various other options. We may want to consider introducing a similar pattern to the Builder, although that may take additional design consideration.

For some background, we need methods of passing in Settings to a Reader or Builder that are instance-local, rather than thread-local. There are numerous reasons why this is needed that have taken place in other discussions. The reason we decided to introduce a ReaderBuilder is because it's impractical and arguably unidiomatic to create or change ~9 of the Reader constructors. It also offers much more flexibility and enables many new permutations of constructing a Reader.

Note that this is only an investigation, we may consider going the other route of providing an Asset struct to encapsulate assets, allowing us to cache a map of the files internals so we don't need to parse it multiple times.

Blocked by:

• feat: Make settings not thread-local #1444
• feat: add settings structs to the public API #1447

[ok-nick]

Still needs docs and tests but marking as ready for further discussion.