timeseries RUM-13949: Add CPU timeseries data-point reader and serializer

[satween]

What does this PR do?

Adds CpuDatapointReader, which reads CPU-usage metrics from the existing CpuVitalReader vital and wraps them as DataPoint values; and CpuEventSerializer, which converts a batch of CPU DataPoints into a RumTimeseriesCpuEvent JSON object ready for ingestion.

Motivation

Implements CPU metric collection as the first concrete timeseries type, exercising the pipeline infrastructure introduced in the previous commit.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)

[satween]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• timeseries RUM-13949 Add end-to-end timeseries verification tests with CSV fixtures #3436
• timeseries RUM-13949 Wire timeseries collection into RUM session lifecycle #3435
• timeseries RUM-13949 Add memory timeseries serializer and session factory #3434
• timeseries RUM-13949: Add CPU timeseries data-point reader and serializer #3433 👈 (View in Graphite)
• timeseries RUM-13949: Implement timeseries pipeline infrastructure #3432
• timeseries RUM-13949: Add timeseries JSON schemas and regenerate API surface #3431
• feature/timeseries

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 90.41096% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.11%. Comparing base (5968d81) to head (75b5891).

Files with missing lines	Patch %	Lines
...internal/timeseries/provider/CpuDatapointReader.kt	79.17%	0 Missing and 5 partials ⚠️
...ternal/timeseries/serializer/CpuEventSerializer.kt	95.92%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@                                       Coverage Diff                                        @@
##           tvaleev/feature/RUM-13949/timeseries-pipeline-infrastructure    #3433      +/-   ##
================================================================================================
- Coverage                                                         72.12%   72.11%   -0.00%     
================================================================================================
  Files                                                               969      971       +2     
  Lines                                                             35515    35588      +73     
  Branches                                                           5905     5920      +15     
================================================================================================
+ Hits                                                              25613    25664      +51     
- Misses                                                             8282     8286       +4     
- Partials                                                           1620     1638      +18     

Files with missing lines	Coverage Δ
...ternal/timeseries/serializer/CpuEventSerializer.kt	95.92% <95.92%> (ø)
...internal/timeseries/provider/CpuDatapointReader.kt	79.17% <79.17%> (ø)

... and 40 files with indirect coverage changes

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