Refactor the types.rs types and structures (#681)

* Refactor the `types.rs` types and structures

A few changes applied along the way:

* Documentation added to most methods and types.
* Limits are now stored with the maximum as optional rather than a
  sentinel u32 value for `None`.
* The `Name` type was removed in favor of just using a bare `String`.
* The `Extern` prefix in the varaints of `ExternType` has been removed
  since it was redundant.
* Accessors of `ExternType` variants no longer panic, and unwrapping
  versions were added with "unwrap" in the name.
* Fields and methods named `r#type` were renamed to `ty` to avoid
  requiring a raw identifier to use them.

* Remove `fail-fast: false`

This was left around since the development of GitHub Actions for
wasmtime, but they're no longer needed!

* Fix compilation of the test-programs code

* Fix compilation of wasmtime-py package

* Run rustfmt

crates/fuzzing/src/oracles/dummy.rs

@@ -13,17 +13,17 @@ pub fn dummy_imports(
 ) -> Result<Vec<Extern>, HostRef<Trap>> {
     let mut imports = Vec::with_capacity(import_tys.len());
     for imp in import_tys {
-        imports.push(match imp.r#type() {
-            ExternType::ExternFunc(func_ty) => {
+        imports.push(match imp.ty() {
+            ExternType::Func(func_ty) => {
                 Extern::Func(HostRef::new(DummyFunc::new(&store, func_ty.clone())))
             }
-            ExternType::ExternGlobal(global_ty) => {
+            ExternType::Global(global_ty) => {
                 Extern::Global(HostRef::new(dummy_global(&store, global_ty.clone())?))
             }
-            ExternType::ExternTable(table_ty) => {
+            ExternType::Table(table_ty) => {
                 Extern::Table(HostRef::new(dummy_table(&store, table_ty.clone())?))
             }
-            ExternType::ExternMemory(mem_ty) => {
+            ExternType::Memory(mem_ty) => {
                 Extern::Memory(HostRef::new(dummy_memory(&store, mem_ty.clone())))
             }
         });