feat: p/subscription

[kazai777]

I've created this subscription package based on this PR from @moul, I've integrated two types of subscription, a recurring payment subscription and a lifetime subscription. Do you have any ideas for other types of subscription that would be relevant to this package?

Contributors' checklist...

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests
• Added new benchmarks to generated graphs, if any. More info here.

[kazai777]

Hi @petar-dambovaliev @harry-hov , can you give me a review when you have time please? Is there anything else I can do to make the review easier for you?

[zivkovicmilos]

Thank you for the package 🙏

I've left some comments alongside @moul, because I think we can make this even better

[zivkovicmilos]

@kazai777 can you please check why the CI is failing? 🙏

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.22%. Comparing base (04d5239) to head (53e11f6).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2116      +/-   ##
==========================================
- Coverage   60.23%   60.22%   -0.01%     
==========================================
  Files         562      562              
  Lines       75091    75091              
==========================================
- Hits        45230    45223       -7     
- Misses      26481    26486       +5     
- Partials     3380     3382       +2     

Flag	Coverage Δ
contribs/gnodev	61.40% <ø> (ø)
contribs/gnofaucet	14.46% <ø> (-0.86%)	⬇️
gno.land	64.76% <ø> (ø)
gnovm	64.33% <ø> (ø)
misc/genstd	80.54% <ø> (ø)
misc/logos	19.88% <ø> (ø)
tm2	62.03% <ø> (-0.02%)	⬇️

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[kazai777]

@kazai777 can you please check why the CI is failing? 🙏

I've fixed the various problems and the CI .

[zivkovicmilos]

Thank you for applying the suggestions 🙏

This now looks super clean 😎