refactor!: refactor installer internals and add new Package class methods (#1523)

This contains the following changes:
1) `Package:install()` now accepts a second, optional, callback argument which is called when installation finishes
   (successfully or not).
2) Adds a `Package:is_installing()` method.

This contains the following breaking changes:
1) `Package:install()` will now error when called while an installation is already ongoing. Use the new
   `Package:is_installing()` method to check whether an installation is already running.

This also refactors large portions of the tests by removing test globals, removing async_test, and adding the
`mason-test` Lua module instead. Test helpers via globals are problematic to work with due to not being detected through
tools like the Lua language server without additional configuration. This has been replaced with a Lua module
`mason-test`. `async_test` has also been removed in favour of explicitly making use of the `mason-core.async` API. These
changes stands for a significant portion of the diff.

1 files changed, 24 insertions, 17 deletions

diff --git a/doc/reference.md b/doc/reference.md
index 2f23e793..ef00425c 100644
--- a/doc/reference.md
+++ b/doc/reference.md
@@ -34,7 +34,8 @@ RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as de
     -   [`Package.License`](#packagelicense)
     -   [`Package.new({spec})`](#packagenewspec)
     -   [`Package.spec`](#packagespec)
-    -   [`Package:install({opts?})`](#packageinstallopts)
+    -   [`Package:is_installing()`](#packageis_installing)
+    -   [`Package:install({opts?}, {callback?})`](#packageinstallopts-callback)
     -   [`Package:uninstall()`](#packageuninstall)
     -   [`Package:is_installed()`](#packageis_installed)
     -   [`Package:get_install_path()`](#packageget_install_path)
@@ -82,12 +83,12 @@ RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as de
 
 The `mason-registry` Lua module extends the [EventEmitter](#eventemitter) interface and emits the following events:
 
-| Event                       | Handler signature                          |
-| --------------------------- | ------------------------------------------ |
-| `package:handle`            | `fun(pkg: Package, handle: InstallHandle)` |
-| `package:install:success`   | `fun(pkg: Package, handle: InstallHandle)` |
-| `package:install:failed`    | `fun(pkg: Package, handle: InstallHandle)` |
-| `package:uninstall:success` | `fun(pkg: Package)`                        |
+| Event                       | Handler signature                                      |
+| --------------------------- | ------------------------------------------------------ |
+| `package:handle`            | `fun(pkg: Package, handle: InstallHandle)`             |
+| `package:install:success`   | `fun(pkg: Package, handle: InstallHandle)`             |
+| `package:install:failed`    | `fun(pkg: Package, handle: InstallHandle, error: any)` |
+| `package:uninstall:success` | `fun(pkg: Package)`                                    |
 
 The following is an example for how to register handlers for events:
 
@@ -135,11 +136,11 @@ The `Package` class encapsulates the installation instructions and metadata abou
 
 This class extends the [EventEmitter](#eventemitter) interface and emits the following events:
 
-| Event               | Handler signature            |
-| ------------------- | ---------------------------- |
-| `install:success`   | `fun(handle: InstallHandle)` |
-| `install:failed`    | `fun(handle: InstallHandle)` |
-| `uninstall:success` | `fun()`                      |
+| Event               | Handler signature                                      |
+| ------------------- | ------------------------------------------------------ |
+| `install:success`   | `fun(handle: InstallHandle)`                           |
+| `install:failed`    | `fun(pkg: Package, handle: InstallHandle, error: any)` |
+| `uninstall:success` | `fun()`                                                |
 
 ### `Package.Parse({package_identifier})`
 
@@ -193,22 +194,28 @@ Similar as [`Package.Lang`](#packagelang) but for SPDX license identifiers.
 
 **Type**: [`RegistryPackageSpec`](#registrypackagespec)
 
-### `Package:install({opts?})`
+### `Package:is_installing()`
+
+**Returns:** `boolean`
+
+### `Package:install({opts?}, {callback?})`
 
 **Parameters:**
 
 -   `opts?`: [`PackageInstallOpts`](#packageinstallopts-1) (optional)
+-   `callback?`: `fun(success: boolean, result: any)` (optional) - Callback to be called when package installation completes. _Note: this is called before events (["package:install:success"](#registry-events), ["install:success"](#package)) are emitted._
 
 **Returns:** [`InstallHandle`](#installhandle)
 
-Installs the package instance this method is being called on. Accepts an
-optional `{opts}` argument, which can be used to specify a desired version to
-install.
+Installs the package instance this method is being called on. Accepts an optional `{opts}` argument which can be used to
+for example specify which version to install (see [`PackageInstallOpts`](#packageinstallopts-1)), and an optional
+`{callback}` argument which is called when the installation finishes.
 
 The returned [`InstallHandle`](#installhandle) can be used to observe progress and control the installation process
 (e.g., cancelling).
 
-_Note that if the package already have an active handle registered, that handler is returned instead of a new one._
+_Note that if the package is already being installed this method will error. See
+[`Package:is_installing()`](#packageis_installing)._
 
 ### `Package:uninstall()`