Remove all global state from the caching system (#863)

* Remove all global state from the caching system

This commit is a continuation of an effort to remove usages of
`lazy_static!` and similar global state macros which can otherwise be
accomodated with passing objects around. Previously there was a global
cache system initialized per-process, but it was initialized in a bit of
a roundabout way and wasn't actually reachable from the `wasmtime` crate
itself. The changes here remove all global state, refactor many of the
internals in the cache system, and makes configuration possible through
the `wasmtime` crate.

Specifically some changes here are:

* Usage of `lazy_static!` and many `static` items in the cache module
  have all been removed.
* Global `cache_config()`, `worker()`, and `init()` functions have all
  been removed. Instead a `CacheConfig` is a "root object" which
  internally owns its worker and passing around the `CacheConfig` is
  required for cache usage.
* The `wasmtime::Config` structure has grown options to load and parse
  cache files at runtime. Currently only loading files is supported,
  although we can likely eventually support programmatically configuring
  APIs as well.
* Usage of the `spin` crate has been removed and the dependency is removed.
* The internal `errors` field of `CacheConfig` is removed, instead
  changing all relevant methods to return a `Result<()>` instead of
  storing errors internally.
* Tests have all been updated with the new interfaces and APIs.

Functionally no real change is intended here. Usage of the `wasmtime`
CLI, for example, should still enable the cache by default.

* Fix lightbeam compilation

Cargo.lock

@@ -1980,7 +1980,6 @@ dependencies = [
  "rayon",
  "serde",
  "sha2",
- "spin",
  "target-lexicon",
  "tempfile",
  "thiserror",