Revise summary.epichains_tree to return <epichains_summary>

[jamesmbaazam]

• Please check if the PR fulfils these requirements

• [x] I have read the CONTRIBUTING guidelines

• [x] The commit message follows our guidelines

• [x] Tests for the changes have been added (for bug fixes / features)

• [x] Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

A feature.

• What is the current behaviour? (You can also link to an open issue here)

summary.epichains_tree method calculates the max generation, number of unique infectors from the <epichains_tree> object.

• What is the new behaviour (if this is a feature change)?

The summary.epichains_tree now returns epichains_summary with the same results as simulate_summary()

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

No, since this package is not released.

• Other information:

This PR closes #119.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.77%. Comparing base (918ee12) to head (fe32c96). Report is 40 commits behind head on main.

:exclamation: Current head fe32c96 differs from pull request most recent head 9e349f0. Consider uploading reports for the commit 9e349f0 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #210 +/- ## ========================================== - Coverage 98.90% 98.77% -0.14% ========================================== Files 8 8 Lines 550 573 +23 ========================================== + Hits 544 566 +22 - Misses 6 7 +1 ```

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[jamesmbaazam]

Super! Just one comment: would it make sense to add a setequal test (as in the example)? That way we can make sure the two implementations don't diverge.

Thanks, that makes sense. I've made the change here 15f10d2180ae80467f0d8c2c4521629d8bf71da7.