Deprecate internal ZstdCompressor constructor

[nhz2]

This adds back in the constructor that was removed in #84 and includes a deprecation warning.

Claude wrote the warning.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.98%. Comparing base (f8c6b20) to head (7f68f91).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/compression.jl	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #85      +/-   ##
==========================================
- Coverage   64.35%   60.98%   -3.37%     
==========================================
  Files           4        4              
  Lines         390      364      -26     
==========================================
- Hits          251      222      -29     
- Misses        139      142       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[mkitti]

Did something come up requiring it?

[nhz2]

No, I think this method can be deleted after the next release.