indexer extension

[rouzwelt]

Motivation

resolves #28

Solution

• create a new folder called rain to include all extension files.
• AlgebraV1Base.ts was already added by us to support algebra based dexes, now it should be moved to newly added rain folder, this equates to 90%+ of the deletions.
• create RainUniswapV2Base.ts and RainUniswapV3Base.ts files in rain folder as an intermediate class between dexes and univ2/3 base classes so some of the base methods can be overridden, these 2 files will inherit from UniswapV2Base.ts and UniswapV3Base.ts which are the original/base files/classes.
• We need to update all the dexes classes in liquidity-providers folder to now inherit from the RainUniswapV2Base.ts and RainUniswapV3Base.ts, so the overrides come into effect when each dex is used.
• Create RainDataFecther in rain folder, this will inherit from original DataFetcher class, but overriding a couple fo its methods to allow for indexer functionality
• add tests for indexer functionalities

Checks

By submitting this for review, I'm confirming I've done the following:

• made this PR as small as possible
• unit-tested any new functionality
• linked any relevant issues or PRs
• included screenshots (if this involves a front-end change)