[gemini] Fix a bug in chunk configuration searching

[Fridge003]

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#4052

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Since the chunk_size attribute in Gemini should be used in number of elements, the modification proposed in #4052 can't be adopted.

Instead, to avoid confusion, arguments including search_range_mb, min_chunk_size_mb and search_interval_bytes should be renamed to search_range_m, min_chunk_size_m and search_interval. In this way, there should be no doubt that chunk_size takes number of elements as its unit rather than number of bytes.

Also, some tests are modified due to this renaming of arguments.

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The code coverage for the changed files is 89%.

Click me to view the complete report

Name                                                                           Stmts   Miss  Cover
--------------------------------------------------------------------------------------------------
colossalai/booster/plugin/gemini_plugin.py                                       110      9    92%
colossalai/zero/gemini/chunk/search_utils.py                                      89      1    99%
colossalai/zero/gemini/chunk/utils.py                                             31      4    87%
colossalai/zero/gemini/gemini_ddp.py                                             402     67    83%
tests/test_auto_parallel/test_tensor_shard/test_compatibility_with_gemini.py      80     80     0%
tests/test_checkpoint_io/test_gemini_checkpoint_io.py                             80      0   100%
tests/test_tensor/test_tp_with_zero.py                                            98      1    99%
tests/test_zero/test_gemini/test_fwd_bwd.py                                      116      1    99%
tests/test_zero/test_gemini/test_gemini_use_rmt.py                                73      1    99%
tests/test_zero/test_gemini/test_grad_clip.py                                     81      1    99%
tests/test_zero/test_gemini/test_inference.py                                     99      1    99%
tests/test_zero/test_gemini/test_optim.py                                        130      1    99%
tests/test_zero/test_gemini/test_search.py                                        70      1    99%
tests/test_zero/test_gemini/test_zeroddp_state_dict.py                            82      5    94%
tests/test_zero/test_gemini/test_zeroddp_state_dict_shard.py                      42      1    98%
tests/test_zero/test_gemini/test_zerooptim_state_dict.py                          67      1    99%
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TOTAL                                                                           1650    175    89%