fix(sdk): panic GrpcContextProvider on async call inside sync code

[lklimek]

Issue being fixed or feature implemented

Two related issues fixed:

1. Tokio::block_on() panics in sync fn in async context:

thread 'main' panicked at 'Cannot start a runtime from within a runtime. This 
happens because a function (like `block_on`) attempted to block the current 
thread while the thread is being used to drive asynchronous tasks.'

2. Proof verification cannot fetch contracts

"proof: the contract could not be retrieved during verification: cannot get data contract: Proof verification error: context provider is not set"

This is caused because we have cyclical dependencies: Sdk uses GrpcContextProvider, and GrpcContextProvider uses Sdk.
Unfortunately, due to the way we initialize GrpcContextProvider, it uses an invalid, not complete copy of Sdk. This issue was introduced in #1838 .

What was done?

Issue 1: Implemented a workaround to safely call async code within sync context. This is done in new spawn_async fn that uses oneshot channel to synchronize with async thread.

Issue 2: Refactored GrpcContextProvider to allow setting sdk without need of &mut. This allows the use of Arc<> when referring to GrpcContextProvider, and helps ensure that it uses correct version of Sdk.

How Has This Been Tested?

GHA

Run dash-sdk tests against local network.

Breaking Changes

None

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have added "!" to the title and described breaking changes in the corresponding section if my code contains any
• I have made corresponding changes to the documentation if needed

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone