Add option to stop advertising vCard 4.0

[0x0f0f0f]

Summary

• Adds [carddav] advertise_vcard4 (default true) so servers shared with macOS Contacts can drop vCard 4.0 from supported-address-data.
• Clients such as DAVx5 write 4.0 whenever the server advertises it; Apple Contacts then rejects those cards and fails the whole address-book sync.
• 4.0 PUTs are still accepted (RFC 6352 only requires accepting advertised versions). Fixes Option to not advertise vCard 4.0 ( macOS Contacts rejects and stops sync) in supported-address-data #265.

Test plan

• cargo test -p rustical_carddav --lib
• Confirm default PROPFIND still lists text/vcard 3.0 and 4.0
• Set advertise_vcard4 = false and confirm PROPFIND lists only 3.0
• PUT a vCard 4.0 with the flag off and confirm the server still accepts it
• With the flag off, create a contact in DAVx5 and confirm macOS Contacts syncs it

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