* net.http.signature: add HTTP Message Signatures (RFC 9421) module
* net.http.signature: pad ECDSA private scalar to curve width when parsing PEM
* net.http.signature: strip default ports from @authority per RFC 9421 §2.2.3
* net.http.signature: reconstruct absolute @target-uri for origin-form requests
* net.http.signature: gate the tests on OpenSSL, like the example and crypto.ecdsa
* net.http.signature: preserve canonical request inputs
* net.http.signature: harden request serialization
* net.http.signature: match transmitted request values
* net.http.signature: align request wire semantics
* net.http.signature: cover effective wire fields
* net.http.signature: validate signing inputs
* net.http.signature: finalize effective message fields
* net.http.signature: validate Ed25519 verification keys
* net.http.signature: validate effective responses
* net.http.signature: reject ambiguous signed messages
* net.http.signature: validate stable wire fields
* net.http.signature: handle remaining wire forms
* net.http.signature: canonicalize repeated inputs
* net.http.signature: validate structured metadata
* net.http.signature: preserve verified message values
* net.http.signature: align status and list parsing
* net.http.signature: tighten parameter parsing
* net.http.signature: preserve extension and empty values
* net.http.signature: preflight transport header changes
* net.http.signature: preserve covered cookie fields
* net.http.signature: trim derived host authority
* net.http.signature: enforce verification coverage
* net.http: preserve wire authorities
* net.http.signature: validate covered fields
* net.http.signature: preserve effective field values
* net.http.signature: enforce verification time bounds
* net.http.signature: align proxy and h2 coverage
* net.http.signature: protect response body defaults
* net.http.signature: protect request body defaults
* net.http.signature: reject invalid response status
* net.http: reject unframed trace bodies
* net.http.signature: load ECDSA public keys from raw coordinates
* net.http.signature: rename a local that collides with hash.crc32's q const
* net.http.signature: make the default digest policy independent of the received body
* net.http.signature: refuse to synthesize a forbidden Content-Length
* net.http.signature: run the tests on the default crypto backend
* net.http.signature: make the quick start verifiable
* net.http.signature: reformat structured_field.v with the current vfmt
* net.http.signature: sharpen the Content-Length diagnostics and document their limits
* net.http.signature: check header capacity at every step of the signing mutations
* net.http.signature: opt the HTTP/2 coverage tests into enable_http2
HTTPS requests default to HTTP/1.1 since #28996, so the tests for covered
fields that HTTP/2 negotiation would change have to enable HTTP/2 themselves.
* net.http: pass the remote address in the new h2 server test
serve_h2_conn takes the remote address since master's HTTP/2 server changes.
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Co-authored-by: Alexander Medvednikov <alexander@medvednikov.com>