feat: calculate simple apy for balancer-aura vaults

[murderteeth]

Related issue: #407

What I did:

I added an apy calculation for balancer-aura vaults. Because this calculation is based on the existing curve-convex calculation I also refactored the existing curve calculation, moving a lot of shared code to yearn/apy/common, yearn/apy/gauge, and yearn/apy/booster.

How I did it:

• Reviewed contracts and documentation on curve, balancer, convex, aura, and a few yearn vaults\strategies.
• Mostly I just followed the curve-convex apy code, adapting for balancer-aura.
• Had some issues with the dev-cycle time in my local environment when using docker. So I modified the debug_apy script to make it easier to use directly with brownie. I also added support for a DISABLE_CURVE envar for disabling the curve exporter during testing. This brought my cycle time down to 15 seconds when computing the bal-aura apy. I mostly ran this while testing: brownie run scripts/debug_apy.py with_exception_handling --network=mainnet

How to verify it:

I used Balancer Boosted Aave USD Pool yVault to test, 0xc5F3D11580c41cD07104e9AF154Fc6428bb93c73. Following is output from the new calculation.

Apy(
  type='aura', 
  gross_apr=0.03632927090500676, 
  net_apy=0.024819477484117503, 
  fees=ApyFees(performance=0.1, withdrawal=None, management=0.0, keep_crv=0.0, cvx_keep_crv=0.0), 
  points=None, 
  blocks=ApyBlocks(now=16711392, week_ago=16661618, month_ago=16489965, inception=15804834), 
  composite={
    'boost': 1.5253965330323664, 
    'bal_rewards_apr': 0.013408715009768951, 
    'aura_rewards_apr': 0.02292055589523781, 
    'extra_rewards_apr': 0, 
    'aura_gross_apr': 0.03632927090500676, 
    'aura_net_apr': 0.02724695317875507, 
    'booster_net_apr': 0.024522257860879564
  }, error_reason=None
)

Check results against the bb-a-usd pool on https://app.aura.finance/, for example:

Checklist:

• I have tested it locally and it works
• I have included any relevant documentation for the repo maintainers
• (If fixing a bug) I have added a test to the test suite to test for this particular bug

Adding a Network

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