Refactor to enforce strictNullChecks

This commit applies `strictNullChecks` to the entire codebase to improve
maintainability and type safety. Key changes include:

- Remove some explicit null-checks where unnecessary.
- Add necessary null-checks.
- Refactor static factory functions for a more functional approach.
- Improve some test names and contexts for better debugging.
- Add unit tests for any additional logic introduced.
- Refactor `createPositionFromRegexFullMatch` to its own function as the
  logic is reused.
- Prefer `find` prefix on functions that may return `undefined` and
  `get` prefix for those that always return a value.

tests/e2e/tsconfig.json

@@ -1,4 +1,5 @@
 {
+  "extends": "../../tsconfig.json",
   "compilerOptions": {
     "target": "es5",
     "lib": [
@@ -8,7 +9,8 @@
     "types": [
       "cypress",
       "node"
-    ]
+    ],
+    "sourceMap": false,
   },
   "include": [
     "**/*.ts"