Use shared slices instead of references to owned vectors as return types

[utpilla]

Changes

• Use shared slices (a more abstract type) instead of references to owned vectors as the return types of TracerProvider.span_processors() and LoggerProvider.log_processors()
• Shared slices offer enough information for the callers of these methods and hides implementation details

Please provide a brief description of the changes here.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.3%. Comparing base (348ec9e) to head (1cde7a3).
Report is 12 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1729     +/-   ##
=======================================
+ Coverage   71.0%   71.3%   +0.3%     
=======================================
  Files        135     136      +1     
  Lines      20751   20840     +89     
=======================================
+ Hits       14746   14879    +133     
+ Misses      6005    5961     -44     

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[cijothomas]

Agree with the change. Please do update changelog with a breaking change warning (affecting plugin authors only), and as a follow up, lets trim all unnecessary public APIs to better handle this in future.

(Assuming this is indeed a breaking change due to pub fn in providers)