[Instrumentation.Process] Update Semantic Conventions to v1.42.0

[martincostello]

Fixes #4089

Changes

Update the process instrumentation to v1.42.0 of the semantic conventions.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.21%. Comparing base (df7fb61) to head (0c0c085).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4602      +/-   ##
==========================================
+ Coverage   77.17%   77.21%   +0.03%     
==========================================
  Files         465      465              
  Lines       19394    19423      +29     
==========================================
+ Hits        14968    14997      +29     
  Misses       4426     4426              

Flag	Coverage Δ
unittests-Instrumentation.Process	100.00% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...elemetry.Instrumentation.Process/ProcessMetrics.cs	100.00% <100.00%> (ø)

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[Copilot]

Pull request overview

Updates OpenTelemetry.Instrumentation.Process to align with OpenTelemetry semantic conventions v1.42.0, including the process.cpu.time attribute rename and adding newly recommended process metrics.

Changes:

• Updated semantic convention version from 1.25.0 to 1.42.0 and renamed process.cpu.state → cpu.mode for process.cpu.time.
• Added new metrics: process.uptime, process.windows.handle.count (Windows only), and process.unix.file_descriptor.count (Linux only).
• Updated tests, README, and changelog to reflect the new metrics and breaking change.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
test/OpenTelemetry.Instrumentation.Process.Tests/ProcessMetricsTests.cs	Updates assertions to include the new metrics and OS-conditional expectations.
src/OpenTelemetry.Instrumentation.Process/README.md	Documents semantic conventions v1.42.0 and adds docs for the new metrics.
src/OpenTelemetry.Instrumentation.Process/ProcessMetrics.cs	Implements new metrics and updates process.cpu.time attributes per v1.42.0.
src/OpenTelemetry.Instrumentation.Process/CHANGELOG.md	Adds an Unreleased entry describing the semantic convention update and breaking change.

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