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, 9 insertions, 12 deletions

diff --git a/tests/mason-core/fs_spec.lua b/tests/mason-core/fs_spec.lua
index 38f97eeb..bd3696da 100644
--- a/tests/mason-core/fs_spec.lua
+++ b/tests/mason-core/fs_spec.lua
@@ -8,17 +8,14 @@ describe("fs", function()
         }
     end)
 
-    it(
-        "refuses to rmrf paths outside of boundary",
-        async_test(function()
-            local e = assert.has_error(function()
-                fs.async.rmrf "/thisisa/path"
-            end)
-
-            assert.equals(
-                [[Refusing to rmrf "/thisisa/path" which is outside of the allowed boundary "/foo". Please report this error at https://github.com/williamboman/mason.nvim/issues/new]],
-                e
-            )
+    it("refuses to rmrf paths outside of boundary", function()
+        local e = assert.has_error(function()
+            fs.sync.rmrf "/thisisa/path"
         end)
-    )
+
+        assert.equals(
+            [[Refusing to rmrf "/thisisa/path" which is outside of the allowed boundary "/foo". Please report this error at https://github.com/williamboman/mason.nvim/issues/new]],
+            e
+        )
+    end)
 end)