fix(common): sanitize dedup redundant capabilities

[SHAcollision]

An app could request capabilities like

/pub/example.com/:rw
/pub/example.com/contacts:w

In this case, /pub/example.com/contacts:w is fully covered by /pub/example.com/:rw . Ideally our Capabilities builder and validator should clean up and sanitise this case.

After the fix, these tests should be satisfied.

    #[test]
    fn redundant_capabilities_builder_dedup() {
        let caps = Capabilities::builder()
            .rw("/pub/example.com/")
            .rw("/pub/example.com/") // Same capability twice
            .write("/pub/example.com/subfolder") // Unnecessary capability, already covered by `/pub/example.com/`
            .finish();
        assert_eq!(caps.to_string(), "/pub/example.com:rw");
    }

    #[test]
    fn redundant_caps_string_dedup() {
        // Repeated capability and unnecessary capability subfolder on the str to parse
        let parsed = Capabilities::try_from("/pub/example.com/:rw,/pub/example.com/:rw,/pub/example.com/subfolder:w").unwrap();
        let caps = Capabilities::builder()
            .rw("/pub/example.com/")
            .finish();
        assert_eq!(caps.to_string(), "/pub/example.com:rw");
        assert_eq!(parsed.to_string(), caps.to_string());
    }