backwards_ecal: add DIS scattered-electron analysis

[mandrenguyen]

Briefly, what does this PR introduce? Please link to any relevant presentations or discussions.

Adds a new benchmark analysis adapted for DIS events, as opposed to the previous one, which is optimized for a particle gun. Here some extra logic is necessary to select the cluster belonging to the scattered electron.
Otherwise the benchmarked quantities are the same:

• Energy response: E_{cluster}/p_{truth}
• Energy resolution versus truth-electron energy, using the same Crystal-Ball/FWHM convention as the particle-gun benchmark
• Position residuals: (x_{cluster}-x_{endpoint}) and (y_{cluster}-y_{endpoint})
• Position resolution versus truth-electron energy, using the central 68% half-width
• Cluster-matching efficiency versus energy

What is the urgency of this PR?

• High (please describe reason below)
• Medium
• [X ] Low

What kind of change does this PR introduce?

• Bug fix (issue #__)
• [X ] New feature (issue #__)
• Optimization (issue #__)
• Updated documentation
• other: __

Please check if any of the following apply

• This PR introduces breaking changes. Please describe changes users need to make below.
• This PR changes default behavior. Please describe changes below.
• AI was used in preparing this PR. Please describe usage below.

AI was used to reformat my pre-existing analysis code to the format expected by the benchmarking.

[veprbl]

Right now this is just a notebook with code to do analysis, not wired to any simulations - not a real benchmark

[mandrenguyen]

I see. Latest commit should trigger the CI I guess. I'm a bit new to this workflow. Let's see.

[veprbl]