fix: Fix the type of the date fields in Attestation at the SDK level

[alainncls]

What does this PR do?

Converts the dates fields back to number (instead of default string)

Related ticket

Fixes #447

Type of change

• Chore
• Bug fix
• New feature
• Documentation update

Check list

• Unit tests for any smart contract change
• Contracts and functions are documented

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (0e7288e) 93.63% compared to head (594f6ac) 93.63%.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #472   +/-   ##
=======================================
  Coverage   93.63%   93.63%           
=======================================
  Files          20       20           
  Lines         330      330           
  Branches       76       76           
=======================================
  Hits          309      309           
  Misses         10       10           
  Partials       11       11           

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