refactor: Simplify and improve code coverage

[SMadani]

Miscellaneous changes aimed at improving test coverage, with added benefits for removing and deprecating unnecessary code.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.01980% with 2 lines in your changes missing coverage. Please review.

Project coverage is 97.83%. Comparing base (fe06b81) to head (6ebadc0).
Report is 76 commits behind head on main.

Files with missing lines	Patch %	Lines
...n/java/com/vonage/client/auth/BasicAuthMethod.java	66.66%	0 Missing and 1 partial ⚠️
...ain/java/com/vonage/client/auth/JWTAuthMethod.java	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #560      +/-   ##
============================================
+ Coverage     95.60%   97.83%   +2.23%     
- Complexity     3427     3907     +480     
============================================
  Files           513      564      +51     
  Lines          8141     8735     +594     
  Branches        451      498      +47     
============================================
+ Hits           7783     8546     +763     
+ Misses          198      136      -62     
+ Partials        160       53     -107     

Files with missing lines	Coverage Δ
...rc/main/java/com/vonage/client/AbstractMethod.java	100.00% <100.00%> (+22.22%)	⬆️
...c/main/java/com/vonage/client/DynamicEndpoint.java	98.62% <100.00%> (+21.86%)	⬆️
src/main/java/com/vonage/client/HttpConfig.java	95.52% <100.00%> (+23.18%)	⬆️
src/main/java/com/vonage/client/Jsonable.java	100.00% <100.00%> (+6.66%)	⬆️
...com/vonage/client/VonageMethodFailedException.java	25.00% <ø> (ø)
...a/com/vonage/client/VonageUnexpectedException.java	75.00% <ø> (ø)
...com/vonage/client/account/FullPricingResponse.java	100.00% <100.00%> (ø)
...ava/com/vonage/client/account/SettingsRequest.java	85.71% <ø> (-14.29%)	⬇️
...com/vonage/client/application/ApplicationList.java	100.00% <100.00%> (+66.66%)	⬆️
...ava/com/vonage/client/auth/AbstractAuthMethod.java	83.33% <100.00%> (ø)
... and 40 more

... and 139 files with indirect coverage changes