[BUG] v1.0.0-dev.12 AliceHttpCall is not immutable

[luiges90]

Describe the bug
AliceHttpCall, AliceHttpRequest and AliceHttpResponse mixins EquatableMixin. The latter is marked @immutable but all Alice classes contains mutable fields, causing lint issues.
The error is:

warning • This class (or a class that this class inherits from) is marked as '@immutable', but one or more of its instance fields aren't final: AliceHttpCall.client, AliceHttpCall.loading, AliceHttpCall.secure, AliceHttpCall.method, AliceHttpCall.endpoint, AliceHttpCall.server, AliceHttpCall.uri,
       AliceHttpCall.duration, AliceHttpCall.request, AliceHttpCall.response, AliceHttpCall.error • lib/models/http_snapshot_call.dart:5:7 • must_be_immutable

To Reproduce
N/A

Expected behavior
AliceHttpCall should be @immutable with only final fields

Screenshots
N/A

Flutter doctor

{10:49}~ ✓ ➭ flutter doctor
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[✓] Network resources

Alice version

• Version: v1.0.0-dev.12

Smartphone (please complete the following information):
N/A

Additional context
Code level issue, not related to any UI.