feat: transfer of subgraphs and curation to L2 through GNS

[pcarranzav]

GIP pending.

This PR would be part of the third stage of The Graph's migration to Arbitrum.

It does the following:

• Add an L1GNS and L2GNS (replacing GNS on each layer), with helper functions to send a subgraph from L1 to L2 with the owner's curation signal.
• L1GNS can also send specific curators' balances for migrated subgraphs to L2 through the bridge.
• L2Curation replaces Curation in L2, removing the bonding curve logic as reserve ratio in L2 is meant to be always 1 (i.e. a flat curve).
• QA improvements across affected files: using explicit imports, re-ordering functions to follow the Solidity style guide, and some gas efficiency changes (e.g. using != 0 instead of > 0 where appropriate)

See GIP-0046 for details: https://forum.thegraph.com/t/gip-0046-l2-migration-helpers/4023

[codecov]

Codecov Report

Patch coverage: 99.44% and project coverage change: +1.84 🎉

Comparison is base (02eedcf) 91.68% compared to head (f1d2599) 93.52%.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #585      +/-   ##
==========================================
+ Coverage   91.68%   93.52%   +1.84%     
==========================================
  Files          40       44       +4     
  Lines        1997     2256     +259     
  Branches      359      401      +42     
==========================================
+ Hits         1831     2110     +279     
+ Misses        166      146      -20     

Flag	Coverage Δ
unittests	93.52% <99.44%> (+1.84%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
contracts/gateway/L1GraphTokenGateway.sol	100.00% <ø> (ø)
contracts/l2/gateway/L2GraphTokenGateway.sol	100.00% <ø> (ø)
contracts/discovery/GNS.sol	98.98% <97.40%> (+9.79%)	⬆️
contracts/curation/Curation.sol	100.00% <100.00%> (ø)
contracts/discovery/L1GNS.sol	100.00% <100.00%> (ø)
contracts/governance/Managed.sol	98.24% <100.00%> (+3.70%)	⬆️
contracts/l2/curation/L2Curation.sol	100.00% <100.00%> (ø)
contracts/l2/discovery/L2GNS.sol	100.00% <100.00%> (ø)
contracts/tests/LegacyGNSMock.sol	100.00% <100.00%> (ø)

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[socket-security]

No dependency changes detected. Learn more about Socket for GitHub ↗︎

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👍 No dependency changes detected in pull request

Pull request alert summary

Issue	Status
Install scripts	✅ 0 issues
Native code	✅ 0 issues
Bin script shell injection	✅ 0 issues
Unresolved require	✅ 0 issues
Invalid package.json	✅ 0 issues
HTTP dependency	✅ 0 issues
Git dependency	✅ 0 issues
Potential typo squat	✅ 0 issues
Known Malware	✅ 0 issues
Telemetry	✅ 0 issues
Protestware/Troll package	✅ 0 issues