[PERF][IMPROVEMENT] argilla server: improve computation for dataset progress and metrics

[frascuchon]

Description

Computing dataset progress and metrics using the search engine drastically reduces the time required to run the Argilla server in HF spaces when persistent storage is enabled.

TODO

• [x] Add search engine tests
• [x] Adapt existing test to mock engine results

Type of change

• Refactor (change restructuring the codebase without changing functionality)
• Improvement (change adding some improvement to an existing functionality)

How Has This Been Tested

Checklist

• I added relevant documentation
• I followed the style guidelines of this project
• I did a self-review of my code
• I made corresponding changes to the documentation
• I confirm My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have added relevant notes to the CHANGELOG.md file (See https://keepachangelog.com/)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 95.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 91.21%. Comparing base (eb6741e) to head (79a578c). Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
...la-server/src/argilla_server/search_engine/base.py	77.77%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #5618 +/- ## =========================================== - Coverage 91.22% 91.21% -0.02% =========================================== Files 145 145 Lines 6051 6065 +14 =========================================== + Hits 5520 5532 +12 - Misses 531 533 +2 ``` | [Flag](https://app.codecov.io/gh/argilla-io/argilla/pull/5618/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=argilla-io) | Coverage Δ | | |---|---|---| | [argilla-server](https://app.codecov.io/gh/argilla-io/argilla/pull/5618/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=argilla-io) | `91.21% <95.00%> (-0.02%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=argilla-io#carryforward-flags-in-the-pull-request-comment) to find out more.

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