feat[test]: more curvefi examples

[AlbertoCentonze]

What I did

Added a comprehensive collection of Curve Finance contracts as examples, ported from curvefi/curve-core to be compatible with Vyper >=0.4.2.

The contracts can be found in tests/functional/examples/thirdparty/curvefi/ organized by functionality:

• AMM implementations (stableswap, tricryptoswap, twocryptoswap)
• Gauge contracts and factories
• Governance contracts (agents, relayers, vault)
• Helper contracts (routers, zaps, rate providers)
• Registry contracts (address provider, metaregistry)
• Legacy contracts moved to legacy/ directory

⚠️ WARNING: It is unsafe to use these contracts in production as they've been ported to Vyper >=0.4.2 without checking their functional equivalence from the original audited version.

How I did it

Ported contracts from the curvefi/curve-core repository, updating them to work with Vyper >=0.4.2 syntax and features.

How to verify it

CI will attempt to compile these contracts as part of the test suite.

Commit message

feat: more curvefi examples

Description for the changelog

Added Curve Finance contract examples ported from curvefi/curve-core for Vyper >=0.4.2 compatibility

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.02%. Comparing base (b74f825) to head (0e35957).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4714      +/-   ##
==========================================
+ Coverage   93.00%   93.02%   +0.01%     
==========================================
  Files         131      131              
  Lines       19095    19095              
  Branches     3324     3324              
==========================================
+ Hits        17760    17763       +3     
  Misses        898      898              
+ Partials      437      434       -3     

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