Add architecture string

[xiazhvera]

Issue #, and/or reason for changes (REQUIRED):

Description of changes:
Extend aws_get_platform_build_os_string to return platform string with architecture information.

String choices follow common industry conventions:

• "Windows" - Microsoft Windows family
• "macOS" - Apple macOS
• "iOS" - Apple iOS
• "tvOS" - Apple tvOS
• "watchOS" - Apple watchOS
• "Android" - Google Android mobile OS
• "BSD" - BSD family (FreeBSD, NetBSD, OpenBSD)
• "Unix" - Unix-like systems (Linux, unix-like etc.)
• "Unknown" - Fallback for unrecognized platforms

Architecture string constants:

• "x86_32" - 32-bit Intel x86 architecture
• "x86_64" - 64-bit Intel x86_64 architecture
• "arm32" - 32-bit ARM architecture
• "arm64" - 64-bit ARM architecture
• "unknown" - Fallback for unrecognized architectures

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

[codecov-commenter]

Codecov Report

❌ Patch coverage is 40.00000% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.07%. Comparing base (192ab0d) to head (364c317).

Files with missing lines	Patch %	Lines
source/system_info.c	40.00%	18 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1227      +/-   ##
==========================================
- Coverage   84.21%   84.07%   -0.14%     
==========================================
  Files          58       58              
  Lines        6093     6116      +23     
==========================================
+ Hits         5131     5142      +11     
- Misses        962      974      +12     

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[sbSteveK]

Can we also leave a description of what this PR is doing in the top box?