Update timeout data type to ulong

[joegoldman2]

Fixes #198.

From the spec, for both PublicKeyCredentialCreationOptions and PublicKeyCredentialRequestOptions:

timeout, of type [unsigned long](https://heycam.github.io/webidl/#idl-unsigned-long)

So I changed the data type to ulong.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ebfd75d) 73.83% compared to head (7d7e118) 73.83%.

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #462   +/-   ##
=======================================
  Coverage   73.83%   73.83%           
=======================================
  Files          99       99           
  Lines        2710     2710           
  Branches      445      445           
=======================================
  Hits         2001     2001           
  Misses        604      604           
  Partials      105      105           

Files	Coverage Δ
Src/Fido2.Models/AssertionOptions.cs	84.21% <100.00%> (ø)
Src/Fido2.Models/CredentialCreateOptions.cs	53.48% <100.00%> (ø)

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.