Investigate Performance: Tradeoff between a shared dict vs separate dict per method.

Creating an issue for the TODO introduced in #17:

https://github.com/RelationalAI-oss/Salsa.jl/blob/705f61017439290bc811e496f0abf1978ac66799/src/default_storage.jl#L59-L67

We should do this investigation then either remove the TODO or make the change.

When this is decided, it'll also affect these functions:
https://github.com/RelationalAI-oss/Salsa.jl/blob/705f61017439290bc811e496f0abf1978ac66799/src/default_storage.jl#L88-L113