use collection that allows more efficient get() in source chain

[thedavidmeister]

current get implementation is slow as it iterates through the whole chain with a filter to implement get.

similar to #35 this is simply due to running everything through a single vector and could be improved by leveraging additional data structures internally

[sphinxc0re]

There is BTreeMap and also HashMap. Are you suggesting one of those?

[thedavidmeister]

@sphinxc0re yes, see the related issues for further discussion

should be able to just have a hash map of pairs based on a custom hashing algo that exposes the header hash as keys + a single top pair

iterator can be built from this to have an index pair

[jamesray1]

[F7-optimization][P7-nicetohave]

[thedavidmeister]

chains are now implemented by whatever persistence backend is configured in the conductor

speed optimisations (e.g. indexing) are up to whatever the storage mechanism can do