How does Cloudflare do HTTPS for my site when I haven't provided them with an ssl certificate?

As NuTTyX as said your name is in the SAN section.

You can see it quickly that way:

$ openssl s_client -connect copyurls.ml:443 -servername copyurls.ml -showcerts </dev/null |& grep -A100 'BEGIN CERTIFICATE' | grep -B100 'END CERTIFICATE' | openssl x509 -text -noout |& grep -A1 'X509v3 Subject Alternative Name'
            X509v3 Subject Alternative Name:
                DNS:sni.cloudflaressl.com, DNS:copyurls.ml, DNS:*.copyurls.ml

Or on the web, go to https://www.ssllabs.com/ssltest/analyze.html?d=copyurls.ml&latest and in the report you can read:

Common names    sni.cloudflaressl.com
Alternative names   sni.cloudflaressl.com copyurls.ml *.copyurls.ml

Nowadays, and rightly so, browsers do not take into account what is in the CN part (at best it is a fallback), it is the SAN part that is relevant, which unfortunately is not shown by default in first page of browsers certificate viewing.

Certificates can be issued for "Subject Alternative Names" (that is, more names that certificate is valid for) which covers your hostname (I've just checked that it covers both your domain and any subdomain). Also, consider that when you censor your browser's navigation bar, the title of the tab still shows the domain name and should be censored as well.