Measure time spent on encoding and the compaction ratio

[masih]

Add metrics to measure time spent on encoding CBOR+ZSTD, and the compaction ratio achieved by ZSTD.

Fixes #863

[codecov]

Codecov Report

Attention: Patch coverage is 74.46809% with 12 lines in your changes missing coverage. Please review.

Project coverage is 67.21%. Comparing base (30fac2e) to head (9f9dfa6).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/encoding/encoding.go	74.46%	9 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #871      +/-   ##
==========================================
- Coverage   67.21%   67.21%   -0.01%     
==========================================
  Files          84       84              
  Lines        9139     9175      +36     
==========================================
+ Hits         6143     6167      +24     
- Misses       2454     2464      +10     
- Partials      542      544       +2     

Files with missing lines	Coverage Δ
internal/encoding/encoding.go	70.11% <74.46%> (+1.48%)	⬆️

... and 3 files with indirect coverage changes

[Stebalien]

Some nits/suggestions but otherwise LGTM