Gracefully handle forgetting grpc_init()

[csvance]

• Forgetting to call grpc_init() now raises an exception instead of hanging
• Allow override of client params for unary rpc like streaming rpc
• rename grpc.events to grpc.sem to make its purpose clear (using a channel as a sem to reduce allocations per request)

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

❌ Patch coverage is 81.25000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.80%. Comparing base (bde341f) to head (594b265).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/Curl.jl	86.66%	2 Missing ⚠️
src/ProtoBuf.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #94      +/-   ##
==========================================
- Coverage   83.83%   83.80%   -0.04%     
==========================================
  Files           7        7              
  Lines         532      531       -1     
==========================================
- Hits          446      445       -1     
  Misses         86       86              

☔ 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.