Refactor get_trace and extend get_opt_trace_by_steps to MOO/constrained

[ltiao]

Summary:
We have a method get_opt_trace_by_steps that was used extensively during our Ax 1.0 benchmarking campaign. It duplicates the basic logic of get_trace but differs in that it operates along (trial_index, MAP_KEY) pairs and respects ordering by timestamp (i.e. chronological order). However, it is limited to single-objective unconstrained problems, and our current needs (multi-objective and/or constrained) have outgrown it. We reconcile the two by extracting three core building blocks of get_trace:

1. _pivot_data_with_feasibility: Pivots data to wide format with feasibility information and metric completeness checks.
2. _compute_trace_values: Computes per-observation trace values (hypervolume for MOO, objective value for SOO), with cumulative best support.
3. _aggregate_and_cumulate_trace: Aggregates values by groups and computes the cumulative best across groups.

These are implemented in a more general way that respects arbitrary groupings and orderings. We then refactor get_trace (and its helpers _prepare_data_for_trace and get_trace_by_arm_pull_from_data) to use these building blocks, and leverage them in get_opt_trace_by_steps to extend its support to multi-objective and constrained problems.

Additionally:

• The timestamp-based sorting in get_opt_trace_by_steps is preserved, which is critical for correct cumulative hypervolume computation (without this, observations would be processed in (trial_index, arm_name, MAP_KEY) order instead of chronological order).
• Tests are updated to replace NotImplementedError checks with actual MOO and constrained test cases that verify correctness of the new functionality.

Differential Revision: D79581270

[meta-codesync]

@ltiao has exported this pull request. If you are a Meta employee, you can view the originating Diff in D79581270.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.76%. Comparing base (8a706b8) to head (e18d69f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4884   +/-   ##
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  Coverage   96.76%   96.76%           
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  Files         591      591           
  Lines       61955    61969   +14     
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+ Hits        59948    59962   +14     
  Misses       2007     2007           

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