Retry more requests; wait longer for Dandiset validity

[jwodder]

As requested here.

(Submitting as a separate PR because it really has nothing to do with what #797 is accomplishing.)

[codecov]

Codecov Report

Merging #798 (f5957fa) into master (2e7be6a) will decrease coverage by 0.16%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #798      +/-   ##
==========================================
- Coverage   85.31%   85.14%   -0.17%     
==========================================
  Files          59       59              
  Lines        6066     6067       +1     
==========================================
- Hits         5175     5166       -9     
- Misses        891      901      +10     

Flag	Coverage Δ
unittests	85.14% <100.00%> (-0.17%)	⬇️

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

Impacted Files	Coverage Δ
dandi/consts.py	100.00% <100.00%> (ø)
dandi/dandiapi.py	92.54% <100.00%> (-0.20%)	⬇️
dandi/dandiarchive.py	82.23% <100.00%> (ø)
dandi/download.py	82.24% <100.00%> (ø)
dandi/support/generatorify.py	0.00% <0.00%> (-16.10%)	⬇️
dandi/_version.py	45.96% <0.00%> (+1.75%)	⬆️

---

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 2e7be6a...f5957fa. Read the comment docs.

[yarikoptic]

thank you! Looks LGTM and since could help to mitigate false fails on CIs for downstream/integration testing done IIRC against releases, I have marked it for release. Let's proceed!