[Refactor] Remove data loader to simplify api

[haochengxia]

• Support loading the trace using TraceReader with S3 URI, e.g.,

   reader = lcs.TraceReader("s3://cache-datasets/cache_dataset_oracleGeneral/2007_msr/msr_hm_0.oracleGeneral.zst")

  As for the cache dir, enable users set it via LCS_HUB_CACHE which is ~/.cache/libcachesim/hub by default.

  • Extra: Detect available disk space before downloading.

• Generate new API reference and docs to show the usage of cache specific params

[haochengxia]

Completed by #33