Use StrategyHelper for safe executions and drop redundant methods

[martintmk]

Details on the issue fix or feature implementation

Just some minor cleanup of internal APIs.

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]

Codecov Report

Merging #1463 (c3941d7) into main (4153d2a) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1463      +/-   ##
==========================================
- Coverage   83.89%   83.89%   -0.01%     
==========================================
  Files         276      275       -1     
  Lines        6495     6493       -2     
  Branches     1015     1015              
==========================================
- Hits         5449     5447       -2     
  Misses        837      837              
  Partials      209      209              

Flag	Coverage Δ
linux	?
macos	83.89% <100.00%> (?)
windows	83.89% <100.00%> (?)

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

Files Changed	Coverage Δ
src/Polly.Core/ResilienceStrategy.cs	100.00% <ø> (ø)
...CircuitBreaker/CircuitBreakerResilienceStrategy.cs	100.00% <100.00%> (ø)
.../Polly.Core/Fallback/FallbackResilienceStrategy.cs	100.00% <100.00%> (ø)
src/Polly.Core/Retry/RetryResilienceStrategy.cs	100.00% <100.00%> (ø)
...rc/Polly.Core/Timeout/TimeoutResilienceStrategy.cs	100.00% <100.00%> (ø)