feat(explore) Add equation support to stats queries

[wmak]

• Follow up to https://github.com/getsentry/sentry/pull/92354, add equation support to the timeseries endpoints

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 99.21875% with 1 line in your changes missing coverage. Please review.

:white_check_mark: All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/sentry/snuba/rpc_dataset_common.py	88.88%	1 Missing :warning:

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #93252    +/-   ##
========================================
  Coverage   87.97%   87.98%            
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  Files       10260    10265     +5     
  Lines      592003   592225   +222     
  Branches    23003    23003            
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+ Hits       520823   521042   +219     
- Misses      70690    70693     +3     
  Partials      490      490