[Enhancement]Support broadcast_object_list in multi-machines & support Searcher running in single GPU

[humu789]

Motivation

fix init bug when running in single GPU #42
fix broadcast_object_list bug, which can not be executed in multi-machines.

Modification

Refactor broadcast_object_list to be consistent with pytorch

BC-breaking (Optional)

1. new broad_object_list is without return value.
2. broad_object_list's parameter changed: object_list -> data

Use cases (Optional)

Examples:
>>> import torch
>>> import mmrazor.core.utils as dist
>>> # non-distributed environment
>>> data = ['foo', 12, {1: 2}]
>>> dist.broadcast_object_list(data)
>>> data
['foo', 12, {1: 2}]
>>> # distributed environment
>>> # We have 2 process groups, 2 ranks.
>>> if dist.get_rank() == 0:
>>> # Assumes world_size of 3.
>>> data = ["foo", 12, {1: 2}] # any picklable object
>>> else:
>>> data = [None, None, None]
>>> dist.broadcast_object_list(data)
>>> data
["foo", 12, {1: 2}] # Rank 0
["foo", 12, {1: 2}] # Rank 1

[codecov]

Codecov Report

Merging #153 (9a4dbd6) into dev_v0.4.0 (7de8a07) will decrease coverage by 0.65%.
The diff coverage is 24.09%.

@@              Coverage Diff               @@
##           dev_v0.4.0     #153      +/-   ##
==============================================
- Coverage       66.17%   65.51%   -0.66%     
==============================================
  Files              92       93       +1     
  Lines            3376     3428      +52     
  Branches          615      630      +15     
==============================================
+ Hits             2234     2246      +12     
- Misses           1040     1080      +40     
  Partials          102      102              

Flag	Coverage Δ
unittests	65.49% <24.09%> (-0.66%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmrazor/core/searcher/evolution_search.py	9.84% <0.00%> (+0.07%)	⬆️
mmrazor/core/searcher/greedy_search.py	12.63% <0.00%> (ø)
mmrazor/core/utils/broadcast.py	21.81% <21.15%> (-7.82%)	⬇️
mmrazor/core/utils/utils.py	29.16% <29.16%> (ø)
mmrazor/core/utils/__init__.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7de8a07...9a4dbd6. Read the comment docs.

[pppppM]

The modification of broadcast_object_list will cause BC-Breaking.
BC-Breaking and Use cases should be added to the PR message.

[pppppM]

A warning needs to be added here

[humu789]

done