Fix EncodingTransformation for Encoding and int instances wrapped in PSObject

[santisq]

Same issue as #34 but when Encoding and int instances are wrapped in PSObject:

$utf8 = [System.Text.Encoding]::UTF8 | Write-Output
Get-ZipEntry .\test.zip | Get-ZipEntryContent -Encoding $utf8

# Get-ZipEntryContent: Cannot process argument transformation on parameter 'Encoding'.
#                      Could not convert input 'System.Text.UTF8Encoding+UTF8EncodingSealed' to a valid Encoding object.

$utf8 = [System.Text.Encoding]::UTF8.CodePage | Write-Output
Get-ZipEntry .\test.zip | Get-ZipEntryContent -Encoding $utf8

# Get-ZipEntryContent: Cannot process argument transformation on parameter 'Encoding'.
#                      Could not convert input '65001' to a valid Encoding object.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.95%. Comparing base (ef826cd) to head (f397433).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #37      +/-   ##
==========================================
+ Coverage   87.92%   87.95%   +0.03%     
==========================================
  Files          36       36              
  Lines        1565     1569       +4     
  Branches      207      207              
==========================================
+ Hits         1376     1380       +4     
  Misses        145      145              
  Partials       44       44              

Flag	Coverage Δ
PS_5.1	87.06% <100.00%> (+0.03%)	⬆️
PS_7_Linux	84.25% <100.00%> (+0.04%)	⬆️
PS_7_Windows	84.63% <100.00%> (+0.03%)	⬆️

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