Reimplement CancellationTokenSourcePool

[martintmk]

Details on the issue fix or feature implementation

This PR changes the way the CancellationTokenSourcePool works to allign better with the .NET 8 TimeProvider.

Unblock further work on #1144

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature
• I have successfully run a local build

[codecov-commenter]

Codecov Report

Merging #1192 (772f598) into main (f4d5347) will increase coverage by 0.05%.
The diff coverage is 100.00%.

❗ Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the Github App Integration for your organization. Read more.

@@            Coverage Diff             @@
##             main    #1192      +/-   ##
==========================================
+ Coverage   83.39%   83.44%   +0.05%     
==========================================
  Files         273      275       +2     
  Lines        6316     6336      +20     
  Branches     1027     1031       +4     
==========================================
+ Hits         5267     5287      +20     
  Misses        844      844              
  Partials      205      205              

Flag	Coverage Δ
linux	?
macos	83.44% <100.00%> (+0.05%)	⬆️
windows	?

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

Impacted Files	Coverage Δ
...Polly.Core/Hedging/Controller/HedgingController.cs	100.00% <100.00%> (ø)
src/Polly.Core/Hedging/Controller/TaskExecution.cs	100.00% <100.00%> (ø)
...rc/Polly.Core/Timeout/TimeoutResilienceStrategy.cs	100.00% <100.00%> (ø)
...re/Utils/CancellationTokenSourcePool.Disposable.cs	100.00% <100.00%> (ø)
...y.Core/Utils/CancellationTokenSourcePool.Pooled.cs	100.00% <100.00%> (ø)
...rc/Polly.Core/Utils/CancellationTokenSourcePool.cs	100.00% <100.00%> (ø)