Reuse odoo guess mimetype code and compatibility code between different versions of python-magic.

Also factorize some code and add comment.

- Introduced a button to dynamically set the expression in the substitution line.
- The feature is available for converters of type "Odoo template", "Odoo template + Evaluation", and "Field".
- Added functionality to visualize how to define each converter, displaying a placeholder (example) for each converter type.
- The code has been designed to ease the integration of additional converters in the future.
- Refactored the code to improve performance and stability.

- Added `ormcache` to improve performance by caching template retrieval
in `_get_cached_template`.
- Refactored template processing logic:
  - Introduced `_to_odoo_template` to centralize transformation
    of external templates into Odoo-compatible format.
  - Simplified template computation in `_compute_template` and
    `_compute_template_data` using cached templates.
- Removed redundant methods (`to_cache`) and consolidated logic for clarity.

fixes the display of the button being quirky
also fix the button vanish when value==False

- Added python-magic to external dependencies in __manifest__.py
- Fixed metadata formatting for print-paper-size in ir_actions_report.py

- the file is correctly computed when fetched from redner
- the file name is standardized.

- Replaced `env.services.user.context` with `user.context`.
- Added import for `user` from `@web/core/user`.