refactor: ProactiveConnect to use DynamicEndpoint

[SMadani]

Same as previous PRs of this kind. Since the API also includes file uploads and downloads, a new interface has been introduced to facilitate binary request bodies in DynamicEndpoint.
There's some other miscellaneous refactoring here too, such as removing previously deprecated classes & methods from public visibility, and migrating all tests to JUnit 5.

[codecov-commenter]

Codecov Report

Merging #489 (e56da34) into main (d9bb181) will increase coverage by 0.02%.
The diff coverage is 86.70%.

@@             Coverage Diff              @@
##               main     #489      +/-   ##
============================================
+ Coverage     93.60%   93.62%   +0.02%     
+ Complexity     2712     2630      -82     
============================================
  Files           409      393      -16     
  Lines          6909     6665     -244     
  Branches        447      429      -18     
============================================
- Hits           6467     6240     -227     
+ Misses          255      252       -3     
+ Partials        187      173      -14     

Files	Coverage Δ
src/main/java/com/vonage/client/BinaryRequest.java	100.00% <100.00%> (ø)
src/main/java/com/vonage/client/HttpWrapper.java	100.00% <ø> (ø)
...com/vonage/client/account/CreateSecretRequest.java	100.00% <ø> (ø)
.../com/vonage/client/account/FullPricingRequest.java	100.00% <ø> (ø)
...om/vonage/client/account/PrefixPricingRequest.java	100.00% <ø> (ø)
...java/com/vonage/client/account/PricingRequest.java	100.00% <ø> (ø)
.../java/com/vonage/client/account/SecretRequest.java	75.00% <ø> (ø)
...n/java/com/vonage/client/account/TopUpRequest.java	87.50% <ø> (ø)
...va/com/vonage/client/auth/SignatureAuthMethod.java	93.33% <ø> (-0.42%)	⬇️
...n/java/com/vonage/client/auth/TokenAuthMethod.java	88.23% <ø> (-0.66%)	⬇️
... and 23 more

... and 2 files with indirect coverage changes