fix: resolve empty UUID startup crash loop

[simonfr]

Resolves #10 and #17.

On initial boot, Plex Media Server tries to look up its device configuration in the database using an empty string ("") for the identifier bind parameter. When the C++ side of PMS handles this empty result (or attempts to parse the returned empty/invalid identifier as a UUID), it throws a Boost/C++ std::domain_error: Invalid uuid length exception, causing an immediate SIGABRT.

How the fix works:

1. Adds an automatic extractor to the Rust interposer that parses Preferences.xml for MachineIdentifier and formats it as a standard 36-character hyphenated UUID.
2. Hooks bind_text / bind_text64 to detect if the query targets the devices table and if the parameter index belongs specifically to the identifier column.
3. If an empty string parameter is bound to identifier, the interposer replaces it on the fly with the parsed formatted UUID from the configuration before forwarding the query to PostgreSQL.
4. Other empty parameters (like name or platform updates on devices) are safely ignored and remain untouched to avoid DB pollution.

Includes Rust unit tests covering the XML parsing and fallback behaviors.