Add more "basic" tests samples to cover supported content types

The new models ("standard_v2_x" and "standard_v3_0") supports 200+ content types: https://github.com/google/magika/tree/main/assets/models/standard_v3_0/README.md

Ideally, we have at least one "basic sample" for each of the supported content types (See `/tests_data/basic/*`).

This issue acts as a call for action -- external help is very welcome!

Important aspects to keep in mind:
- Content types for which we have no samples yet should be prioritized. Among these, prioritize more common content types rather than niche ones.
- The "basic" test samples (in the `tests_data/basic//*`) are supposed to be "easy to recognize". In other words, the goal for these samples is to check that the model does a reasonable job with clear-cut samples, rather than corner-cases.
- It's OK to group a bunch of test cases in a single PR.
- The PR should state the origin of each sample.
- The samples should NOT be taken from existing projects / online resources (in these settings, it would be very challenging to properly document the origin of these files); they should be manually written/created by the PR author.

Start by reading the supported content types in assets/models/standard_v3_0/README.md and inspecting tests_data/basic//* for missing samples. Create clear, manually written samples for common unsupported content types, and record each sample's origin in the PR. Done means the new samples are included in the appropriate basic-test directories without using files from existing projects or online resources.

Written by the indexing model from the issue text.