Add types for charged/neutral particle candidates

[ruse-traveler]

Briefly, what does this PR introduce?

This PR introduces the {Charged,Neutral}RecoParticleCandidate types. Similar in spirit to the edm4eic::ProtoCluster, these types consolidate the necessary track, cluster, and PID relations ahead of any reconstruction of a particle's kinematics and properties.

What kind of change does this PR introduce?

• Bug fix (issue #__)
• New feature (issue Proposal for a PseudoParticle type #97 )
• Documentation update
• Other: __

Please check if this PR fulfills the following:

• Tests for the changes have been added
• Documentation has been added / updated
• Changes have been communicated to collaborators

Does this PR introduce breaking changes? What changes might users need to make to their code?

No.

Does this PR change default behavior?

No.

[ruse-traveler]

Leaving this as draft for now while discussion progresses.

[ruse-traveler]

Based on discussions and developments in EDM4eic#122, EICrecon#2078, and epic#994, epic#994 should provide the minimum functionality needed to complete PFAlpha.

In light of this, I believe this PR can be closed and revisited later if need be.

[wdconinc]

This was closed but in case it gets revived: could this not have been addressed with a subset collection, which avoids data duplication and has (therefore) a smaller footprint?

[ruse-traveler]

This was closed but in case it gets revived: could this not have been addressed with a subset collection, which avoids data duplication and has (therefore) a smaller footprint?

Hmmm... Maybe! But I'm having trouble seeing how we might go about it. The first idea that comes to me is to create a subset of clusters, tracks, etc. for each particle candidate...