chore(retentions): add new retentions method for support drafts

[raul-facturapi]

No description provided.

[Copilot]

Pull request overview

Adds first-class support for draft retentions in the .NET SDK by exposing new wrapper methods and routing helpers, along with behavioral tests and a package version bump.

Changes:

• Added retention draft operations to the Retention wrapper/API: UpdateDraftAsync, StampDraftAsync, and CopyToDraftAsync.
• Extended RetentionRouter with the corresponding routes for draft update/stamp/copy.
• Added wrapper behavior tests covering draft listing, draft creation payload, and the new draft routes; bumped package version and updated changelog.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Wrappers/RetentionWrapper.cs	Implements the new draft retention methods (PUT update, POST stamp, POST copy) and response deserialization.
Wrappers/IRetentionWrapper.cs	Exposes the new draft retention methods on the public wrapper interface.
Router/RetentionRouter.cs	Adds route builders for updating/stamping/copying retention drafts.
FacturapiTest/WrapperBehaviorTests.cs	Adds route/payload assertions for draft retentions behavior and the new wrapper methods.
facturapi-net.csproj	Bumps package version to 6.6.0.
CHANGELOG.md	Documents the 6.6.0 release and the added draft retention methods.

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