Move batch size to LitAPI

[aniketmaurya]

What does this PR do?

Batch size is closely attached to LitAPI for batched processing. LitServer doesn't make any use of this value.

Decoupling batch size and batch timeout from LitServer will help in enabling multiple endpoints with a cleaner architecture.

Old

api = LitAPI()
server = LitServer(api, max_batch_size=4)

New

(We still allow providing max_batch_size in LitServer with a deprecation warning - SS below)

api = LitAPI(max_batch_size=4)
server = LitServer(api)

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

Attention: Patch coverage is 91.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89%. Comparing base (509a301) to head (7cbece5).
Report is 2 commits behind head on main.

Additional details and impacted files

@@         Coverage Diff         @@
##           main   #468   +/-   ##
===================================
- Coverage    89%    89%   -0%     
===================================
  Files        37     37           
  Lines      2158   2163    +5     
===================================
+ Hits       1913   1917    +4     
- Misses      245    246    +1     

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