JSONRPC.jl: move implementation to LSP.jl internal scope

[aviatesk]

The current implementation of JSONRPC.jl is actually LSP-dependent and does not suit the generic name "JSONRPC". Therefore, it would be better to keep that implementation internal to LSP.jl.

[codecov]

Codecov Report

❌ Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.27%. Comparing base (a718c6c) to head (9b6b0ea).
⚠️ Report is 1 commits behind head on avi/JSON-v1-again.

Files with missing lines	Patch %	Lines
src/testrunner/testrunner.jl	0.00%	2 Missing ⚠️
src/JETLS.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                  Coverage Diff                  @@
##           avi/JSON-v1-again     #303      +/-   ##
=====================================================
- Coverage              66.28%   66.27%   -0.01%     
=====================================================
  Files                     39       39              
  Lines                   4096     4095       -1     
=====================================================
- Hits                    2715     2714       -1     
  Misses                  1381     1381              

☔ 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.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.