feat(nano): implement contract accessor

[glevco]

Motivation

Implement a new API for interacting with contracts. For now, it just supports interacting with view and public methods from other contracts.

# Before
self.syscall.call_public_method(other_id, ‘my_public_method’, [action1, action2], a=‘abc’)

# After
self.syscall.get_contract(other_id) \
    .prepare_public_call(action1, action2) \
    .my_public_method(a=‘abc’)

Acceptance Criteria

• Add HATHOR_TOKEN_UID constant to allowed imports on blueprints.
• Implement get_contract syscall to be used in blueprint methods. It returns a ContractAccessor instance which is a wrapper for a contract and a runner, allowing blueprints to call methods of other contracts directly on that instance, instead of using manual syscalls.
  • All existing runner protections are still in place. This is just a new layer of abstraction on top of syscalls.
• Update the test_types_across_contracts.py test to use the new API, as a demo.

Unresolved Discussions

• The new API currently does not support fallback methods, and instead will fail the tx if the method is not found. Let's keep the related discussion in this thread: feat(nano): implement contract accessor #1382 (comment)

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged

[github-actions]

Bencher Report

Branch	feat/nano/contract-accessor
Testbed	ubuntu-22.04

🚨 1 Alert

Benchmark	Measure Units	View	Benchmark Result (Result Δ%)	Upper Boundary (Limit %)
sync-v2 (up to 20000 blocks)	Latency minutes (m)	📈 plot 🚷 threshold 🚨 alert (🔔)	2.16 m (+28.89%) Baseline: 1.68 m	2.01 m (107.41%)

Click to view all benchmark results

Benchmark	Latency	Benchmark Result minutes (m) (Result Δ%)	Lower Boundary minutes (m) (Limit %)	Upper Boundary minutes (m) (Limit %)
sync-v2 (up to 20000 blocks)	📈 view plot 🚷 view threshold 🚨 view alert (🔔)	2.16 m (+28.89%) Baseline: 1.68 m	1.51 m (69.83%)	2.01 m (107.41%)

🐰 View full continuous benchmarking report in Bencher

[codecov]

Codecov Report

❌ Patch coverage is 99.20635% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 85.83%. Comparing base (482fec5) to head (be586f6).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
hathor/nanocontracts/runner/runner.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1382      +/-   ##
==========================================
+ Coverage   85.81%   85.83%   +0.02%     
==========================================
  Files         429      430       +1     
  Lines       32453    32570     +117     
  Branches     5057     5072      +15     
==========================================
+ Hits        27850    27957     +107     
- Misses       3586     3593       +7     
- Partials     1017     1020       +3     

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[jansegre]

I really like the API. I don't really like the prepare_view_call and prepare_public_call names, maybe they are too long. But I don't have a better suggestion. I'm OK with going with those for now.