add stats per key interceptor

[wyfo]

I chose in the end to use an interceptor instead of reusing the existing stat incrementing code because it was a lot easier to reuse the interceptor caching system than build a new one (that must support runtime invalidation and regeneration).

[github-actions]

PR missing one of the required labels: {'documentation', 'dependencies', 'enhancement', 'internal', 'bug', 'new feature', 'breaking-change'}

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 70.85%. Comparing base (e5a13a9) to head (a2c26e5).
⚠️ Report is 23 commits behind head on main.

Files with missing lines	Patch %	Lines
zenoh/src/net/routing/interceptor/mod.rs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2146      +/-   ##
==========================================
- Coverage   70.88%   70.85%   -0.04%     
==========================================
  Files         375      375              
  Lines       63218    60819    -2399     
==========================================
- Hits        44814    43091    -1723     
+ Misses      18404    17728     -676     

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