py-shared: cross-region chunksums support (pass scratch bucket map to lambdas)

[nl0]

Changes required for cross-region chunksums (passing the scratch bucket map to the lambdas):

• Add scratch_buckets required field to S3HashLambdaParams
• Introduce PackageConstructParams

TODO

• Changelog entry (skip if change is not significant to end users, e.g. docs only)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 36.58%. Comparing base (2edbba0) to head (2c50da7).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3922   +/-   ##
=======================================
  Coverage   36.58%   36.58%           
=======================================
  Files         719      719           
  Lines       31980    31980           
  Branches     4707     4707           
=======================================
  Hits        11700    11700           
  Misses      19116    19116           
  Partials     1164     1164           

Flag	Coverage Δ
api-python	90.89% <ø> (ø)
catalog	10.61% <ø> (ø)
lambda	87.74% <ø> (ø)

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