Refactors CPP Client into library

[vsreekanti]

• Elevates user CLI/benchmark client logic into client.hpp. This enables us to use the client as an import elsewhere.
• Refactors CLI and benchmark to use the client library.
• Adds client library support for durable puts (put_all), get_all, and set-based operations.
• Removes client only methods from the HashRingUtil interface (and moves them into the client library).

[codecov[bot]]

Codecov Report

Merging #65 into master will increase coverage by 2.87%. The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master      #65      +/-   ##
==========================================
+ Coverage      64%   66.88%   +2.87%     
==========================================
  Files          50       48       -2     
  Lines        1603     1531      -72     
==========================================
- Hits         1026     1024       -2     
+ Misses        577      507      -70

Impacted Files	Coverage Δ
kvs/include/common.hpp	78.12% <ø> (-1.29%)	:arrow_down:
kvs/include/utils/server_utils.hpp	65.78% <ø> (ø)	:arrow_up:
kvs/src/kvs/rep_factor_response_handler.cpp	1.53% <ø> (+0.01%)	:arrow_up:
kvs/include/hash_ring.hpp	91.3% <ø> (ø)	:arrow_up:
kvs/src/kvs/gossip_handler.cpp	6.97% <ø> (+0.15%)	:arrow_up:
kvs/src/hash_ring/hash_ring.cpp	0% <0%> (ø)	:arrow_up:
kvs/tests/kvs/server_handler_base.hpp	100% <100%> (ø)	:arrow_up:
include/zmq/zmq_util.cpp
kvs/include/threads.hpp	76.08% <0%> (+3.17%)	:arrow_up:

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