Drop allocations when using ResilienceProperties

[martintmk]

Details on the issue fix or feature implementation

Add a type check for a plain dictionary to avoid enumerator allocation.

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 #1276 (22279f1) into main (a908391) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1276   +/-   ##
=======================================
  Coverage   83.33%   83.33%           
=======================================
  Files         270      270           
  Lines        6317     6320    +3     
  Branches      981      983    +2     
=======================================
+ Hits         5264     5267    +3     
  Misses        844      844           
  Partials      209      209           

Flag	Coverage Δ
linux	83.33% <100.00%> (+<0.01%)	⬆️
macos	83.33% <100.00%> (+<0.01%)	⬆️
windows	?

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Impacted Files	Coverage Δ
src/Polly.Core/ResilienceProperties.cs	100.00% <100.00%> (ø)