fix the search

[YONN2222]

This pull request improves the resilience and flexibility of the MediathekShow model and enhances the networking layer for Mediathek API interactions. The main changes include making the size property optional and more robust in its decoding, updating related logic to handle optional sizes, and improving the network layer with custom session configuration and better error/debug logging.

Model robustness and decoding improvements:

• Changed the size property in MediathekShow from a non-optional Int to an optional Int?, and updated its decoding logic to handle both numeric and string representations, as well as missing values. [1] [2] [3]
• Updated encoding and usage of size throughout the codebase to handle the optional case, including in encoding/decoding, download size calculation, and persistence logic. [1] [2] [3]

Networking improvements:

• Refactored MediathekAPI to use a custom URLSession configuration that disables caching, sets timeouts, and enables waits for connectivity. Also added detailed debug logging for requests, responses, and errors, and improved error handling for decoding and network failures.

Project configuration:

• Updated the project version in Zapp.xcodeproj/project.pbxproj from 15 to 16. [1] [2]