feat(storage): experimental options to tune stall timeouts

[coryan]

Some applications need more progress than just "at least 1 byte per
second for K seconds". These new options allow them to require "at
least N bytes per second for K seconds".

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This change is 

[google-cloud-cpp-bot]

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[codecov]

Codecov Report

Merging #9593 (f5f371f) into main (3c0781d) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #9593      +/-   ##
==========================================
- Coverage   94.35%   94.34%   -0.01%     
==========================================
  Files        1491     1491              
  Lines      137714   137750      +36     
==========================================
+ Hits       129935   129967      +32     
- Misses       7779     7783       +4     

Impacted Files	Coverage Δ
google/cloud/internal/curl_impl.h	100.00% <ø> (ø)
...gle/cloud/storage/internal/curl_download_request.h	100.00% <ø> (ø)
google/cloud/storage/internal/curl_request.h	100.00% <ø> (ø)
...ogle/cloud/storage/internal/curl_request_builder.h	53.57% <ø> (ø)
google/cloud/internal/curl_impl.cc	89.73% <100.00%> (-0.14%)	⬇️
google/cloud/storage/client_options.cc	88.26% <100.00%> (+0.40%)	⬆️
google/cloud/storage/client_options_test.cc	100.00% <100.00%> (ø)
...le/cloud/storage/internal/curl_download_request.cc	87.62% <100.00%> (-0.97%)	⬇️
google/cloud/storage/internal/curl_request.cc	100.00% <100.00%> (ø)
...gle/cloud/storage/internal/curl_request_builder.cc	92.07% <100.00%> (+0.50%)	⬆️
... and 10 more

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[devbww]

#include <cstdint>

[Aside: Do we support L32 platforms? FWIW, uint32_t -> long would then be implementation-defined on large values.]

[coryan]

Fixed.

Yes, we support Windows in 64-bit mode, which is LLP64 (long is 32-bits), and Windows in 32-bit mode. I forgot about the sign bit, fixed.

[google-cloud-cpp-bot]

Google Cloud Build Logs
For commit: f5f371f116643822898c974704eff8e6a1282baa

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