feature: client v2

[fregataa]

refs lablup/backend.ai#1772, lablup/backend.ai#1784

Implement client_v2

• Let any data including key and value serialized(and deserialized) from the client side.
• Disallow *-prefix requests since they need string typed key. Instead, you can use *-range requests.
• Does not use EtcdRequestGenerator because there is no complicated request building logic anymore such as parsing range_end to support -prefix functionalities.

[codecov]

Codecov Report

Attention: 316 lines in your changes are missing coverage. Please review.

Comparison is base (5b512ef) 53.00% compared to head (ae98864) 47.04%.

Files	Patch %	Lines
src/etcetra/v2/client.py	0.00%	309 Missing ⚠️
src/etcetra/v2/types.py	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #24      +/-   ##
==========================================
- Coverage   53.00%   47.04%   -5.96%     
==========================================
  Files          37       39       +2     
  Lines        2496     2812     +316     
==========================================
  Hits         1323     1323              
- Misses       1173     1489     +316     

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