refactor(logs): remove UNSTABLE prefix from feature flag

[lcian]

Renaming UNSTABLE_logs to logs.

Reasoning:

• other SDKs are already shipping it without experimental
• The only changes I see we would make to the API is extensions, such as allowing more types to be passed in or additional syntax to call e.g. the Display or Debug impl as in tracing. For this purpose, types can remain the same, only the macros would change under the hood to allow for these extensions.
• UNSTABLE might lead to people not using the feature

#skip-changelog

[codecov]

Codecov Report

Attention: Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.

Project coverage is 72.84%. Comparing base (3e82901) to head (7d618d0).

Additional details and impacted files

@@                       Coverage Diff                       @@
##           lcian/feat/logs-batching-clean     #832   +/-   ##
===============================================================
  Coverage                           72.84%   72.84%           
===============================================================
  Files                                  64       64           
  Lines                                7733     7733           
===============================================================
  Hits                                 5633     5633           
  Misses                               2100     2100           

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