Fix issues in pass_util.cc password handling

[justsmth]

Description of changes:

Addresses multiple issues in tool-openssl/pass_util.cc and the Password class:

• Ensured all temporary buffers holding passwords are properly cleansed, including the buf stack buffer in ExtractPasswordFromStream and a std::string replaced with Password for secure clearing.
• Fixed fd: parsing to use strtoul instead of atoi, avoiding undefined behavior on overflow.
• Removed incorrect rejection of colons in pass: passwords, matching OpenSSL behavior.
• Fixed off-by-one in password length limits for pass: and env: sources.
• Minor hardening: fixed same_file initialization, replaced unsigned subtraction with overflow-safe comparison in ExtractDirectPassword.

Call-outs:

• Behavioral change: pass:a:b was previously rejected and now succeeds with password a:b.

Testing:

All existing PassUtilTest tests pass. Updated DirectPasswordEdgeCases to cover passwords containing colons.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 88.23529% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.18%. Comparing base (107e67d) to head (e963dc1).

Files with missing lines	Patch %	Lines
tool-openssl/pass_util.cc	84.61%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3032      +/-   ##
==========================================
- Coverage   78.19%   78.18%   -0.01%     
==========================================
  Files         689      689              
  Lines      121822   121825       +3     
  Branches    16995    16994       -1     
==========================================
- Hits        95254    95251       -3     
- Misses      25684    25690       +6     
  Partials      884      884              

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