Add metadata support for HTTP.URI

Fixes #402: `metadata(HTTP.URI(...))` now works the same way
`load(HTTP.URI(...))` already did.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ViralBShah

ext/HTTPExt.jl

@@ -9,5 +9,6 @@ else
 end
 
 FileIO.load(uri::HTTP.URI) = load(IOBuffer(HTTP.get(uri).body))
+FileIO.metadata(uri::HTTP.URI) = metadata(IOBuffer(HTTP.get(uri).body))
 
 end # module