Requestmodel refactor

[badnikhil]

PR Description

Key Changes:

1. Created the ProtocolModel sealed class union (rest, graphql, ai).
2. Removed direct httpRequestModel and aiRequestModel fields from RequestModel and replaced them with the protocolModel wrapper.
3. Updated collection_providers.dart to safely navigate and update state using .mapOrNull().
4. Migrated Dashbot's chat_viewmodel.dart to become protocol-aware so it doesn't accidentally attempt to modify non-HTTP requests.
5. Regenerated all *.freezed.dart and *.g.dart files and updated all test fixtures.

Related Issues

• Closes #

Checklist

• I have gone through the contributing guide
• I have updated my branch and synced it with project main branch before making this PR
• I am using the latest Flutter stable branch (run flutter upgrade and verify)
• I have run the tests (flutter test) and all tests are passing

Added/updated tests?

We encourage you to add relevant test cases.

• Yes
• No, and this is why: please replace this line with details on why tests have not been included

OS on which you have developed and tested the feature?

• Windows
• macOS
• Linux

[badnikhil]

@animator TODO: implement backward compatibility to support older versions of saved requests.