[Exporter.Prometheus] Nullable

[ysolomchenko]

Towards https://github.com/open-telemetry/opentelemetry-dotnet/issues/3958

Changes

• Exporter.Prometheus.HttpListener marked as nullable
• Exporter.Prometheus.AspNetCore marked as nullable

Merge requirement checklist

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

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 86.22%. Comparing base (6250307) to head (46e5fed). Report is 314 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5791      +/-   ##
==========================================
+ Coverage   83.38%   86.22%   +2.84%     
==========================================
  Files         297      257      -40     
  Lines       12531    11166    -1365     
==========================================
- Hits        10449     9628     -821     
+ Misses       2082     1538     -544     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	86.19% <100.00%> (?)
unittests-Project-Stable	86.21% <100.00%> (?)
unittests-UnstableCoreLibraries-Experimental	85.76% <100.00%> (?)

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

Files with missing lines	Coverage Δ
...ometheus.AspNetCore/PrometheusAspNetCoreOptions.cs	50.00% <100.00%> (-25.00%)	:arrow_down:
.../PrometheusExporterApplicationBuilderExtensions.cs	100.00% <ø> (ø)
...rometheusExporterEndpointRouteBuilderExtensions.cs	100.00% <ø> (ø)
...rometheusExporterMeterProviderBuilderExtensions.cs	100.00% <ø> (ø)
...metheus.AspNetCore/PrometheusExporterMiddleware.cs	73.17% <100.00%> (+3.17%)	:arrow_up:
...tpListener/Internal/PrometheusCollectionManager.cs	86.20% <100.00%> (+8.42%)	:arrow_up:
...etheus.HttpListener/Internal/PrometheusExporter.cs	100.00% <100.00%> (ø)
...s.HttpListener/Internal/PrometheusHeadersParser.cs	100.00% <ø> (ø)
...ometheus.HttpListener/Internal/PrometheusMetric.cs	74.12% <100.00%> (+2.37%)	:arrow_up:
...heus.HttpListener/Internal/PrometheusSerializer.cs	86.85% <100.00%> (+1.98%)	:arrow_up:
... and 3 more

... and 214 files with indirect coverage changes

[github-actions[bot]]

This PR was marked stale due to lack of activity and will be closed in 7 days. Commenting or pushing will instruct the bot to automatically remove the label. This bot runs once per day.

[github-actions[bot]]

This PR was marked stale due to lack of activity and will be closed in 7 days. Commenting or pushing will instruct the bot to automatically remove the label. This bot runs once per day.

[TimothyMothra]

@rajkumar-rangaraj, we need a Prometheus expert to help with this review. There's a lot of changes I'm unsure about.