Rethink interaction of all conda-related tooling in conda-store

[nkaretnikov]

Context

@jaimergp suggested I open this for discussing long-term plans for conda-store with regard to how conda tools are used.
Right now, we use conda as a library, via conda-lock, and via constructor.
All these know nothing about each other (only implicitly, e.g., via a shared global conda cache), which might lead to problems.
For example, #745 (comment) was discovered because conda-store and conda-lock didn't communicate, so the shared cache was not used, which led to everything being downloaded on every build.

Value and/or benefit

Better performance and reliability.

Anything else?

No response