Fix logging of step runtime statistics

[berland]

This had to be moved to _ensemble.py as the state inside _snapshot.py only had information about steps that fell into the same batching window, thus long lasting steps would have start_time=None

Issue
Resolves #my_issue

Approach
Short description of the approach

(Screenshot of new behavior in GUI if applicable)

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure unit tests pass locally after every commit (git rebase -i main --exec 'pytest tests/ert/unit_tests -n logical -m "not integration_test"')

When applicable

• When there are user facing changes: Updated documentation
• New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• Large PR: Prepare changes in small commits for more convenient review
• Bug fix: Add regression test for the bug
• Bug fix: Create Backport PR to latest release

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 90.72%. Comparing base (c077aad) to head (d415f44).

Files with missing lines	Patch %	Lines
src/ert/ensemble_evaluator/_ensemble.py	87.50%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9121      +/-   ##
==========================================
- Coverage   90.73%   90.72%   -0.02%     
==========================================
  Files         350      350              
  Lines       21781    21787       +6     
==========================================
+ Hits        19764    19766       +2     
- Misses       2017     2021       +4     

Flag	Coverage Δ
cli-tests	39.03% <87.50%> (-0.01%)	⬇️
gui-tests	71.70% <87.50%> (+0.01%)	⬆️
performance-tests	49.24% <81.25%> (+<0.01%)	⬆️
unit-tests	79.58% <87.50%> (+<0.01%)	⬆️

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[sondreso]

We try again 🚀