Track RPC v2 CBOR feature

[arandito]

Description

This PR adds support for tracking usage of the PROTOCOL_RPC_V2_CBOR feature.

User agent strings can now include an 'M' in the m/ metrics field when an operation is called using the Smithy RPC v2 CBOR protocol.

User agent string example:

Boto3/1.37.9 md/Botocore#1.37.9 ua/2.1 os/macos#24.3.0 md/arch#arm64 lang/python#3.12.8 md/pyimpl#CPython m/M cfg/retry-mode#legacy Botocore/1.37.9

See #3389 for more details on client feature tracking.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.97%. Comparing base (6300f6b) to head (228b96e).
Report is 50 commits behind head on develop.

Files with missing lines	Patch %	Lines
botocore/args.py	50.00%	1 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3422      +/-   ##
===========================================
+ Coverage    92.94%   92.97%   +0.02%     
===========================================
  Files           66       67       +1     
  Lines        14956    15056     +100     
===========================================
+ Hits         13901    13998      +97     
- Misses        1055     1058       +3     

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