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 72.85%. Comparing base (c4fe8fb) to head (68a3cf7).
Report is 1 commits behind head on lcian/feat/logs-batching-clean.

Additional details and impacted files

@@                        Coverage Diff                         @@
##           lcian/feat/logs-batching-clean     #832      +/-   ##
==================================================================
+ Coverage                           72.84%   72.85%   +0.01%     
==================================================================
  Files                                  64       64              
  Lines                                7732     7732              
==================================================================
+ Hits                                 5632     5633       +1     
+ Misses                               2100     2099       -1     

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[Swatinem]

on the one hand, it would be good to publish a release with this still marked as UNSTABLE.
but on the other hand, we are far far away from having any kind of API (semver) stability, so it probably doesn’t matter anyway.