JLSEC-2026-611 Unbounded HTTP/2 concurrent streams and Rapid Reset denial of service in HTTP.jl server

Description The HTTP.jl HTTP/2 server advertised an empty initial SETTINGS frame, leaving SETTINGSMAXCONCURRENTSTREAMS effectively unlimited, and the HEADERS code path allocated per-stream state, a send-window entry, and a Threads.@spawned handler with no check on the number of open streams...