306 rework attachments in interaction for better dev

[PandaGuerrier]

This pull request refactors and simplifies the handling of media assets and file attachments throughout the codebase. The main focus is on introducing a new Asset class to unify the representation of media files, replacing older classes and patterns, and updating related components and utilities to use this new abstraction.

Key changes include:

Media Asset Abstraction and Refactoring:

• Introduced a new Asset class in asset.dart to represent media assets, supporting construction from files and providing a consistent toJson interface. ([lib/src/api/common/components/asset.dartR1-R53](https://github.com/mineral-dart/core/pull/308/files#diff-3fbbfd1a71c21b0da772f58f73fc1b0182a879136d2daa58247dad63b495895cR1-R53))
• Refactored MessageGallery and MessageThumbnail to use the new Asset class instead of custom GalleryItem and MessageMedia classes, and removed those now-obsolete classes. ([[1]](https://github.com/mineral-dart/core/pull/308/files#diff-0fdf1ae2b9b8e602b0b3f0891e59f4816b3d55d643beb10bf3fddd73f6929b97L1-R8), [[2]](https://github.com/mineral-dart/core/pull/308/files#diff-0fdf1ae2b9b8e602b0b3f0891e59f4816b3d55d643beb10bf3fddd73f6929b97L19-L81), [[3]](https://github.com/mineral-dart/core/pull/308/files#diff-b525cb54063745dbe2f6788352f43c9739fd84c1d8ac0b2373691ca4da3f42ddL1-L15), [[4]](https://github.com/mineral-dart/core/pull/308/files#diff-8f28f0b16ea988f78630dfe810fd3531d01a5566c3452dd52f22b4ae9fb9586fR5-R13))

File Attachment Handling:

• Renamed and refactored the file attachment class from Attachment to MessageFile, simplifying its API and removing caching logic. Updated the file method in MessageBuilder to use MessageFile. ([[1]](https://github.com/mineral-dart/core/pull/308/files#diff-51664875c1f9dfced04f6ef0abd776771dedd208d062aaeaafa2198925f52cdcL7-R27), [[2]](https://github.com/mineral-dart/core/pull/308/files#diff-c826a76b7e732d8d76753211299eb15d5083b70a77bc3f8b2e1395d9ef2b7977L79-R79))
• Updated exports in api.dart to reflect the new and removed classes, ensuring the public API is consistent with these changes. ([lib/api.dartR30-L37](https://github.com/mineral-dart/core/pull/308/files#diff-af9ff7cdb71adcd379123b2b2de8b383941c39b54a0cb1a07dc784ccb0aae6c1R30-L37))

Attachment Utilities Update:

• Refactored the attachment utility in attachment.dart to handle the new Asset structure, updating how multipart files are prepared and attached for both files and gallery/media assets. ([[1]](https://github.com/mineral-dart/core/pull/308/files#diff-1737ee8ca6e3b58944c539226c2955ec393db6d878b4388d752a58542d4ffea2L4-R4), [[2]](https://github.com/mineral-dart/core/pull/308/files#diff-1737ee8ca6e3b58944c539226c2955ec393db6d878b4388d752a58542d4ffea2L17-R73))

Overall, these changes modernize and streamline the way media and files are handled in messages, making the codebase easier to maintain and extend.

[DCodeProg]

Nice 👍