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/unit/presentation/components/Shared/Hooks/Clipboard/BrowserClipboard.spec.ts

@@ -2,6 +2,7 @@ import { describe, it, expect } from 'vitest';
 import { BrowserClipboard, NavigatorClipboard } from '@/presentation/components/Shared/Hooks/Clipboard/BrowserClipboard';
 import { StubWithObservableMethodCalls } from '@tests/unit/shared/Stubs/StubWithObservableMethodCalls';
 import { expectThrowsAsync } from '@tests/shared/Assertions/ExpectThrowsAsync';
+import { expectExists } from '@tests/shared/Assertions/ExpectExists';
 
 describe('BrowserClipboard', () => {
   describe('writeText', () => {
@@ -16,7 +17,7 @@ describe('BrowserClipboard', () => {
       const calls = navigatorClipboard.callHistory;
       expect(calls).to.have.lengthOf(1);
       const call = calls.find((c) => c.methodName === 'writeText');
-      expect(call).toBeDefined();
+      expectExists(call);
       const [actualText] = call.args;
       expect(actualText).to.equal(expectedText);
     });

tests/unit/presentation/components/Shared/Hooks/Clipboard/UseClipboard.spec.ts

@@ -3,6 +3,7 @@ import { useClipboard } from '@/presentation/components/Shared/Hooks/Clipboard/U
 import { BrowserClipboard } from '@/presentation/components/Shared/Hooks/Clipboard/BrowserClipboard';
 import { ClipboardStub } from '@tests/unit/shared/Stubs/ClipboardStub';
 import { FunctionKeys } from '@/TypeHelpers';
+import { expectExists } from '@tests/shared/Assertions/ExpectExists';
 
 describe('useClipboard', () => {
   it(`returns an instance of ${BrowserClipboard.name}`, () => {
@@ -41,7 +42,7 @@ describe('useClipboard', () => {
           // assert
           testFunction(...expectedArgs);
           const call = clipboardStub.callHistory.find((c) => c.methodName === functionName);
-          expect(call).toBeDefined();
+          expectExists(call);
           expect(call.args).to.deep.equal(expectedArgs);
         });
         it('ensures method retains the clipboard instance context', () => {