Enable _claim_admin_fees for CurveCryptoPool

[allt0ld]

Description

Closes #231.

Enabled _claim_admin_fees for CurveCryptoPool. For maintainability, tricrypto_ng.vy's implementation and usage patterns are used for both 2-coin and 3-coin Cryptoswap pools. 2-coin CurveCryptoPool and cryptopool.vy will diverge primarily by calling _claim_admin_fees with different timings; any calculations involved are largely the same. I expect that differences relative to the 2-coin vyper contract's behavior will average out to a negligible amount over the course of a sim pipeline.

However, if CurveCryptoPool needs to simulate gulping, then the above solution will not be viable. One potential solution, as @chanhosuh says, would be to implement the following:

"Organize all these [CurveCryptoPool] functions by a sort of configuration based on pool version that specifies when [_claim_admin_fees] or [_tweak_price] should be called. Then it's enforced by a function that checks what method it is in and what version the pool is."

Alternatively, adding statements like if self.n == 2 or if self.n == 3 to the functions that call _claim_admin_fees in either one of tricrypto_ng.vy or cryptopool.vy (_tweak_price, add_liquidity, remove_liquidity, and remove_liquidity_one_coin) plus _claim_admin_fees itself could work. Of course, these solutions are tricky and messy, but there's no going around that.

Hygiene checklist

• Changelog entry
• Everything public has a Numpy-style docstring
  (modules, public functions, classes, and public methods)
• Commit history is cleaned-up with minor changes squashed together
  and descriptive commit messages following Tim Pope's style

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curvesim/pool/cryptoswap/pool.py

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