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, 46 insertions, 0 deletions

diff --git a/lua/mason-core/installer/context/spawn.lua b/lua/mason-core/installer/context/spawn.lua
new file mode 100644
index 00000000..6528c4b3
--- /dev/null
+++ b/lua/mason-core/installer/context/spawn.lua
@@ -0,0 +1,46 @@
+local spawn = require "mason-core.spawn"
+
+---@class InstallContextSpawn
+---@field strict_mode boolean Whether spawn failures should raise an exception rather then return a Result.
+---@field private cwd InstallContextCwd
+---@field private handle InstallHandle
+---@field [string] async fun(opts: SpawnArgs): Result
+local InstallContextSpawn = {}
+
+---@param cwd InstallContextCwd
+---@param handle InstallHandle
+---@param strict_mode boolean
+function InstallContextSpawn.new(cwd, handle, strict_mode)
+    return setmetatable({ cwd = cwd, handle = handle, strict_mode = strict_mode }, InstallContextSpawn)
+end
+
+---@param cmd string
+function InstallContextSpawn:__index(cmd)
+    ---@param args JobSpawnOpts
+    return function(args)
+        args.cwd = args.cwd or self.cwd:get()
+        args.stdio_sink = args.stdio_sink or self.handle.stdio.sink
+        local on_spawn = args.on_spawn
+        local captured_handle
+        args.on_spawn = function(handle, stdio, pid, ...)
+            captured_handle = handle
+            self.handle:register_spawn_handle(handle, pid, cmd, spawn._flatten_cmd_args(args))
+            if on_spawn then
+                on_spawn(handle, stdio, pid, ...)
+            end
+        end
+        local function pop_spawn_stack()
+            if captured_handle then
+                self.handle:deregister_spawn_handle(captured_handle)
+            end
+        end
+        local result = spawn[cmd](args):on_success(pop_spawn_stack):on_failure(pop_spawn_stack)
+        if self.strict_mode then
+            return result:get_or_throw()
+        else
+            return result
+        end
+    end
+end
+
+return InstallContextSpawn