feat(): fix unary, math, and conditional operatiors + test updates (#277)

* move `NullishShortCircuit` to its own file, and clean up some lint rules
* fully working unit tests with fixed evaluation for unary/binary/math operators + cleanup

Author: TroyAlford

.vscode/settings.json

@@ -0,0 +1,10 @@
+{
+	"eslint.format.enable": true,
+	"editor.codeActionsOnSave": {
+		"source.organizeImports": "always",
+		"source.fixAll.eslint": "always",
+		"source.fixAll.tslint": "always",
+		"source.fixAll.ts": "always",
+	},
+	"files.insertFinalNewline": true
+}