Send call request without requiring await

[slawlor]

This change addresses #343

Here we will immediately trigger the message send, deferring the receive future. In the previous version, even the send will wait for the caller to poll the future, which means the "send" may not occur right away, and this is somewhat counter intuitive.

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 2 lines in your changes missing coverage. Please review.

Project coverage is 80.62%. Comparing base (9e5d24b) to head (a1ef000).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
ractor/src/rpc/mod.rs	85.71%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #345   +/-   ##
=======================================
  Coverage   80.61%   80.62%           
=======================================
  Files          66       66           
  Lines       13244    13247    +3     
=======================================
+ Hits        10677    10680    +3     
  Misses       2567     2567           

☔ 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.