refactor(targets): use get_url util for subpaths

[dan-online]

Description

Fixes path joining in:

• Emby/Jellyfin
• Autopulse
• Fileflows
• Plex
• Tdarr

Closes #149

Type of change

• Bug (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (addition or change to documentation)

Technical

Parsed urls technically kept their path but unless the original url ended in a "/", future join calls would override instead of- join

fn get_url(&self) -> anyhow::Result<url::Url> {
    let url = if self.url.ends_with('/') {
        self.url.clone()
    } else {
        format!("{}/", self.url)
    };

    url::Url::parse(&url).map_err(Into::into)
}

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