Rename Dictionary.php to DictionaryInterface.php

[tacman]

It appears that most interface classes use the Interface suffix.

This will be even more relevant if #154 is implemented.

[ErwannRousseau]

Renaming Dictionary to DictionaryInterface would improve API clarity, especially now that #154 introduces named autowiring such as DictionaryInterface $voteDictionary.

However, this is a public API change rather than an architectural refactoring. A direct rename would break existing type hints, custom dictionary implementations, and the named autowiring aliases introduced by #154.

A backward-compatible migration could be:

1. Introduce DictionaryInterface.
2. Keep Dictionary as a deprecated compatibility interface.
3. Support autoconfiguration and named autowiring for both types.
4. Prefer DictionaryInterface in the documentation.
5. Remove Dictionary in the next major version.

I would therefore keep this separate from #154 and implement it through a deprecation cycle, unless a v4 release is planned.

[tacman]

DictionaryInterface $voteDictionary.

except that Symfony now recommends #[Target] instead of using names.

[ErwannRousseau]

👀 PR #370 to close #154