Deep scanners: PKCS improvement and Java .class container

[babenek]

Description

Please include a summary of the change and which is fixed.

• Add Java .class file deep scanner for constants which are Utf8 strings
• Improved PKCS scanner for PKCS#1, PKCS#8 and PKCS#12 keys
• refactored PEM private key detection

How has this been tested?

Please describe the tests that you ran to verify your changes.

• UnitTest
• Benchmark

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 87.11656% with 21 lines in your changes missing coverage. Please review.

Project coverage is 92.68%. Comparing base (8579630) to head (a56f20f).
Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
credsweeper/deep_scanner/jclass_scanner.py	85.18%	5 Missing and 3 partials ⚠️
credsweeper/deep_scanner/pkcs_scanner.py	72.00%	5 Missing and 2 partials ⚠️
credsweeper/utils/util.py	95.16%	1 Missing and 2 partials ⚠️
credsweeper/deep_scanner/deep_scanner.py	85.71%	0 Missing and 2 partials ⚠️
credsweeper/filters/value_base64_key_check.py	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #716      +/-   ##
==========================================
- Coverage   92.80%   92.68%   -0.12%     
==========================================
  Files         141      142       +1     
  Lines        5127     5222      +95     
  Branches      841      855      +14     
==========================================
+ Hits         4758     4840      +82     
- Misses        228      235       +7     
- Partials      141      147       +6     

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