Function https_h3_client_config 

pub fn https_h3_client_config(roots: RootCertStore) -> ClientConfig

HTTP/3-ALPN rustls client config over the given trust roots (DW-108): the shared shape for every outbound H3/QUIC dial — the H3 upstream connector and the QUIC active health probe. QUIC mandates TLS 1.3, so this always negotiates h3 over the same root store the pooled https connector would use (#121: webpki by default, the upstream’s trusted_ca_file bundle when configured). Keeping the constructor here means one trust/handshake policy across the pooled H3 client and its probes, mirroring https_h1_client_config.