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.

[gpeacock]

This should be set_external_manifest(), otherwise it looks like a getter in Rust.

[gpeacock]

We are generally moving away from CaiRead and CaiWrite as we don't need them anymore. But since this function already uses CAIRead, I think this is ok here.

[gpeacock]

I think this could be done as a ReaderAsset and include format and stream.

then we can call something like this on Reader

pub fn from_reader_asset(
    settings: &Settings,
    asset: ReaderAsset,
) -> Result<Reader> {
    let format = asset.format;
    let stream = asset.stream;
    if let Some(external_manifest) = asset.external_manifest {
        if let Some(fragments) = asset.fragments {
            Self::from_fragment(
                &format,
                stream,
                external_manifest,
                fragments,
            )
        } else {
            Self::from_manifest_data_and_stream(
                &jumbf_io::read_to_end(external_manifest)?,
                &format,
                stream,
            )
        }
    } else {
        Self::from_stream(&format, stream)
    }
}

[magaylor]

Are there currently plans to expose this object to the c2pa_c_ffi path? I would love to be able to access this from binding code.