feat!: rs-sdk is thread safe and doesn't require &mut

[lklimek]

Issue being fixed or feature implemented

rs-sdk should not require mutable references, as it complicates usage of the Sdk.
For example,it might require locking.

What was done?

We use Arc and lock inside Sdk whenever required.

Also some smaller refactorings implemented, for example:

• added CancellationToken to allow cancelling of execution
• refactored ContextProvider mock as GrpcContextProvider

How Has This Been Tested?

Breaking Changes

• SdkBuilder::build() returns Arc
• You need to explicitly provide ContextProvider

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

[shumkov]

I think we should extract context logic from this PR and keep only thread safe stuff

[shumkov]

Nice improvement 👍