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

crates/environ/src/cache/tests.rs

@@ -36,11 +36,9 @@ fn test_cache_init() {
     );
     fs::write(&config_path, config_content).expect("Failed to write test config file");
 
-    let errors = init(true, Some(&config_path), None);
-    assert!(errors.is_empty());
+    let cache_config = CacheConfig::from_file(Some(&config_path)).unwrap();
 
     // test if we can use config
-    let cache_config = cache_config();
     assert!(cache_config.enabled());
     // assumption: config init creates cache directory and returns canonicalized path
     assert_eq!(
@@ -53,8 +51,7 @@ fn test_cache_init() {
     );
 
     // test if we can use worker
-    let worker = worker();
-    worker.on_cache_update_async(config_path);
+    cache_config.worker().on_cache_update_async(config_path);
 }
 
 #[test]
@@ -69,7 +66,6 @@ fn test_write_read_cache() {
         cache_dir
     );
     assert!(cache_config.enabled());
-    let worker = Worker::start_new(&cache_config, None);
 
     // assumption: config load creates cache directory and returns canonicalized path
     assert_eq!(
@@ -102,7 +98,6 @@ fn test_write_read_cache() {
         compiler1,
         false,
         &cache_config,
-        &worker,
     ));
     assert!(entry1.0.is_some());
     assert!(entry1.get_data().is_none());
@@ -117,7 +112,6 @@ fn test_write_read_cache() {
         compiler1,
         false,
         &cache_config,
-        &worker,
     ));
     let data2 = new_module_cache_data(&mut rng);
     entry2.update_data(&data2);
@@ -131,7 +125,6 @@ fn test_write_read_cache() {
         compiler1,
         false,
         &cache_config,
-        &worker,
     ));
     let data3 = new_module_cache_data(&mut rng);
     entry3.update_data(&data3);
@@ -146,7 +139,6 @@ fn test_write_read_cache() {
         compiler1,
         false,
         &cache_config,
-        &worker,
     ));
     let data4 = new_module_cache_data(&mut rng);
     entry4.update_data(&data4);
@@ -162,7 +154,6 @@ fn test_write_read_cache() {
         compiler2,
         false,
         &cache_config,
-        &worker,
     ));
     let data5 = new_module_cache_data(&mut rng);
     entry5.update_data(&data5);