feat: Add contacts database and VFS implementation

- Added a new contacts database (`ContactsDB`) to store contact
  information.  This improves data organization and allows for
  more efficient querying and manipulation of contact data.
- Implemented a virtual file system (VFS) for contacts
  (`vfs_contacts`). This provides a file-like interface to access
  and manage contact data, improving integration with existing
  file-system-based tools and workflows.  The VFS supports
  listing by group, by name, and by email.
- Added model structs for contacts, improving data organization and
  serialization.  This lays the foundation for more robust data
  handling and future expansion.

lib/vfs/vfs_mail/factory.v

@@ -1,7 +1,7 @@
 module vfs_mail
 
 import freeflowuniverse.herolib.vfs
-import freeflowuniverse.herolib.circles.dbs.core
+import freeflowuniverse.herolib.circles.mcc.db as core
 
 // new creates a new mail VFS instance
 pub fn new(mail_db &core.MailDB) !vfs.VFSImplementation {