feat(cli): When invoked with only a schema file (no instances), validates the schema against its meta-schema

[Stranger6667]

Ref #804

[codecov]

Codecov Report

❌ Patch coverage is 98.13084% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.94%. Comparing base (8b7491e) to head (fe59d50).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
crates/jsonschema-cli/src/main.rs	96.15%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #873      +/-   ##
==========================================
+ Coverage   93.92%   93.94%   +0.02%     
==========================================
  Files          78       78              
  Lines       16026    16131     +105     
==========================================
+ Hits        15052    15154     +102     
- Misses        974      977       +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.

[codspeed-hq]

CodSpeed Performance Report

Merging #873 will not alter performance

_{Comparing dd/cli-meta (fe59d50) with master (8b7491e)}

Summary

✅ 61 untouched