Feat: add support for custom cache dir in Streaming Dataset

[bhimrazy]

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?

What does this PR do?

Fixes #398.

• Adds support for custom cache dir in Streaming Dataset

Usage

import litdata as ld

dataset = ld.StreamingDataset(input_dir = 's3://my-bucket/fast_data', cache_dir='local_cache_dir' ,shuffle=True, drop_last=True)

PR review

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78%. Comparing base (62907b3) to head (20be9e1).
Report is 1 commits behind head on main.

Additional details and impacted files

@@         Coverage Diff         @@
##           main   #399   +/-   ##
===================================
  Coverage    78%    78%           
===================================
  Files        34     34           
  Lines      5042   5045    +3     
===================================
+ Hits       3948   3954    +6     
+ Misses     1094   1091    -3