feat: implementation of expected hypervolume improvement

[aaronkl]

Implements expected hypervolume improvement, a popular Bayesian optimization strategy for multi-objective problems using the BOTorch implementation. It also fixes a small bug in the FIFO scheduler.

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov]

Codecov Report

Attention: 72 lines in your changes are missing coverage. Please review.

Comparison is base (0597dfc) 64.31% compared to head (73245f5) 64.28%.

Files	Patch %	Lines
...ultiobjective/expected_hyper_volume_improvement.py	55.69%	70 Missing ⚠️
syne_tune/optimizer/baselines.py	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #825      +/-   ##
==========================================
- Coverage   64.31%   64.28%   -0.03%     
==========================================
  Files         441      442       +1     
  Lines       29306    29475     +169     
==========================================
+ Hits        18848    18948     +100     
- Misses      10458    10527      +69     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.