Improve security and reliability of macOS updates

This commit introduces several improvements to the macOS update process,
primarily focusing on enhancing security and reliability:

- Add data integrity checks to ensure downloaded updates haven't been
  tampered with.
- Optimize update progress logging in `streamWithProgress` by limiting
  amount of logs during the download process.
- Improve resource management by ensuring proper closure of file
  read/write streams.
- Add retry logic with exponential back-off during file access to handle
  occassionally seen file system preparation delays on macOS.
- Improve decision-making based on user responses.
- Improve clarity and informativeness of log messages.
- Update error dialogs for better user guidance when updates fail to
  download, unexpected errors occur or the installer can't be opened.
- Add handling for unexpected errors during the update process.
- Move to asynchronous functions for more efficient operation.
- Move to scoped imports for better code clarity.
- Update `Readable` stream type to a more modern variant in Node.
- Refactor `ManualUpdater` for improved separation of concerns.
- Document the secure update process, and log directory locations.
- Rename files to more accurately reflect their purpose.
- Add `.DS_Store` in `.gitignore` to avoid unintended files in commits.

README.md

@@ -179,4 +179,6 @@ Check [architecture.md](./docs/architecture.md) for an overview of design and ho
 
 ## Security
 
-Security is a top priority at privacy.sexy. An extensive commitment to security verification ensures this priority. For any security concerns or vulnerabilities, please consult the [Security Policy](./SECURITY.md).
+Security is a top priority at privacy.sexy.
+An extensive commitment to security verification ensures this priority.
+For any security concerns or vulnerabilities, please consult the [Security Policy](./SECURITY.md).