ae.utils.json: Add support for floating point

Also simplify some D1 remnant code
ae.net.ietf.headers: Fix const-correctness, add unittest
ae.net.http: Move range handling into server module

Also switch back to a full read when serving files until we can have
reference-counted response objects.
[BREAKING] ae.net.http.responseex: Remove short-lived serveFile overload
ae.sys.net.test: Add license header, module statement