get cargo-deny to be quiet

[svix-jbrown]

Changes:

• remove now-unused advisory about rustls-webpki
• upgrade rand to deal with RUSTSEC-2026-0097 and remove that from the list
• add unused-ignored-advisory, unused-allowed-license, unused-license-exception, and unused-allowed-source so cargo-deny doesn't warn us about things that only apply to one subproject
• fill in the allow-git key
• remove unused license clarifications
• fill in the license field for bridge

after this change:

$ for dir in bridge server svix-cli rust ; cd $dir ; cargo deny check -c ../deny.toml ; cd .. ; end
advisories ok, bans ok, licenses ok, sources ok
advisories ok, bans ok, licenses ok, sources ok
advisories ok, bans ok, licenses ok, sources ok
advisories ok, bans ok, licenses ok, sources ok