Preserve unknown/GREASE HTTP/2 SETTINGS entries in Akamai fingerprint output

[Copilot]

Chrome sends a GREASE-like HTTP/2 SETTINGS entry that was being dropped from TrackMe’s Akamai fingerprint output. This made TrackMe diverge from real Chrome SETTINGS fingerprints when unknown setting IDs were present.

• Problem

  • getSettingsFingerprint only mapped known setting names.
  • UNKNOWN_SETTING_<id> entries (including GREASE IDs) produced empty/malformed fingerprint segments.

• Change

  • Added fallback handling for UNKNOWN_SETTING_<id> in /pkg/http/fingerprint_h2.go.
  • When a setting name is unknown but matches that pattern, the numeric <id> is parsed and emitted as the setting key in the fingerprint.
  • Invalid unknown-setting identifiers now fail closed with the existing "error" output path.

• Targeted coverage

  • Added unit tests in /pkg/http/fingerprint_h2_test.go for:
    • preserving unknown/GREASE IDs in fingerprint serialization,
    • rejecting malformed unknown-setting identifiers.

settingID := mapping[parts[0]]
if settingID == "" && strings.HasPrefix(parts[0], "UNKNOWN_SETTING_") {
    rawID := strings.TrimPrefix(parts[0], "UNKNOWN_SETTING_")
    if _, err := strconv.ParseUint(rawID, 10, 16); err != nil {
        return "error"
    }
    settingID = rawID
}

• Fixes HTTP/2 SETTINGS frame is missing the GREASE entry real Chrome sends #46