Indifferent to b64url padding in indy-utils

[gmulhearn-anonyome]

it was found that recent updates to base64 in indy-utils made the codebase less resilient to b64url padding when decoding. Previously we were indifferent to padding when decoding, then a regression was made which made indy-utils REQUIRE padding. This PR fixes the regression such that indy-utils will decode with or without padding.

this is important for utils such as unpack_message.

according to encryption envelope: https://github.com/hyperledger/aries-rfcs/blob/main/features/0019-encryption-envelope/README.md

NOTE: In the unpack algorithm, the base64url decode implementation used MUST correctly decode padded and unpadded base64URL encoded data.

[codecov-commenter]

Codecov Report

Merging #1055 (79a5c3e) into main (ed4ee6b) will not change coverage.
Report is 1 commits behind head on main.
The diff coverage is 0.00%.

@@          Coverage Diff          @@
##            main   #1055   +/-   ##
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  Coverage   0.05%   0.05%           
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  Files        379     379           
  Lines      20912   20912           
  Branches    3853    3853           
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  Hits          12      12           
  Misses     20899   20899           
  Partials       1       1           

Flag	Coverage Δ
unittests-aries-vcx	0.05% <0.00%> (ø)

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Files	Coverage Δ
...rtools/indy-utils/src/crypto/base64/rust_base64.rs	0.00% <0.00%> (ø)