Improve metrics for find/chat/ask

[lferran]

Description

This pr adds:

• recording of first generative chunk yield metric
• improve how we report slow queries

How was this PR tested?

Describe how you tested this PR.

[github-actions]

Benchmark

Benchmark suite	Current: 607b5e5	Previous: 08db1e8	Ratio
nucliadb/search/tests/unit/search/test_fetch.py::test_highligh_error	3019.6507854914644 iter/sec (stddev: 0.000006726336266689788)	3041.132211072051 iter/sec (stddev: 0.0000011628635974660105)	1.01

This comment was automatically generated by workflow using github-action-benchmark.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.16%. Comparing base (b551226) to head (9bffe44).
Report is 5 commits behind head on main.

❗ Current head 9bffe44 differs from pull request most recent head 607b5e5

Please upload reports for the commit 607b5e5 to get more accurate results.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2216      +/-   ##
==========================================
+ Coverage   77.15%   77.16%   +0.01%     
==========================================
  Files          94       94              
  Lines        6045     6044       -1     
==========================================
  Hits         4664     4664              
+ Misses       1381     1380       -1     

Flag	Coverage Δ
ingest	71.48% <ø> (+0.02%)	⬆️

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