Set LitServer.stream using LitSpec.stream

[aniketmaurya]

What does this PR do?

Users will be able to create their own Spec and define streaming behavior for their Spec.

Fixes #397

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91%. Comparing base (fcce973) to head (373c8b4).
Report is 1 commits behind head on main.

Additional details and impacted files

@@         Coverage Diff         @@
##           main   #398   +/-   ##
===================================
  Coverage    91%    91%           
===================================
  Files        25     25           
  Lines      1777   1782    +5     
===================================
+ Hits       1622   1627    +5     
  Misses      155    155