refactor(types): traversal_paths is now a comma-sep string

[hanxiao]

Based on the considerations:

• less nested-structure in argument
• numpy.einsum's subscript https://numpy.org/doc/stable/reference/generated/numpy.einsum.html

[codecov]

Codecov Report

Merging #3925 (958dca1) into master (5915342) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3925      +/-   ##
==========================================
- Coverage   88.88%   88.84%   -0.04%     
==========================================
  Files         176      176              
  Lines       12376    12384       +8     
==========================================
+ Hits        11000    11003       +3     
- Misses       1376     1381       +5     

Flag	Coverage Δ
daemon	43.70% <9.09%> (-0.01%)	⬇️
jina	86.91% <100.00%> (-0.04%)	⬇️

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

Impacted Files	Coverage Δ
jina/types/arrays/mixins/traverse.py	90.27% <100.00%> (-0.35%)	⬇️
jina/peapods/peas/__init__.py	84.57% <0.00%> (-2.66%)	⬇️
jina/peapods/runtimes/jinad/__init__.py	80.86% <0.00%> (-1.74%)	⬇️
jina/peapods/runtimes/zmq/zed.py	90.86% <0.00%> (-0.46%)	⬇️
jina/peapods/pods/__init__.py	85.65% <0.00%> (+0.22%)	⬆️
jina/clients/base/__init__.py	88.57% <0.00%> (+1.42%)	⬆️
jina/importer.py	87.17% <0.00%> (+2.56%)	⬆️

---

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[github-actions]

Latency summary

Current PR yields:

• 🐢🐢 index QPS at 1246, delta to last 2 avg.: -6%
• 🐢🐢 query QPS at 52, delta to last 2 avg.: -12%
• 🐢🐢 dam extend QPS at 35565, delta to last 2 avg.: -10%
• 🐢🐢 avg flow time within 1.5855 seconds, delta to last 2 avg.: +36%
• 😶 import jina within 0.4539 seconds, delta to last 2 avg.: +2%

Breakdown

Version	Index QPS	Query QPS	DAM Extend QPS	Avg Flow Time (s)	Import Time (s)
current	1246	52	35565	1.5855	0.4539
2.4.3	1337	56	37766	1.2398	0.4647
2.4.2	1316	62	42125	1.0865	0.4174

Backed by latency-tracking. Further commits will update this comment.