Create base `ReadHyperdrive` interface with common methods from integrations

[ryangoree]

The ReadHyperdrive interface doesn't currently, but should include:

• getSharesToken
• convertToBase
• convertToShares

[ryangoree]

A default impl of getSharesToken can be created using the new vaultSharesToken field of IHyperdrive.PoolConfig: delvtech/hyperdrive#892

[ryangoree]

These have all been implemented.