Add proof-measure client (public securedBy / measured-immutability service)

proof-measure is a separate, public, unauthenticated Dragonchain service. Adds:
- client.UnauthenticatedClient: HMAC-free transport mirroring Client's
  marshal/decode/error handling.
- proofmeasure.ProofMeasureClient: GetSecurity / Report / Health, default base
  URL https://proof-measure.dragonchain.com; standalone + a DragonchainSDK.ProofMeasure handle.
- models for SecurityResult/RawMeasure/ReportRequest/TransactionReport/etc
  (decimals as strings, timestamps int64).
- httptest unit tests.

models/models.go

@@ -206,3 +206,84 @@ type InterchainTrace struct {
 	ValidatorBlocks        []VerificationBlock     `json:"validatorBlocks"`
 	InterchainTransactions []InterchainTransaction `json:"interchainTransactions"`
 }
+
+// --- proof-measure service (measured immutability / "securedBy") ---
+//
+// Decimal-valued fields are transmitted as strings (full precision); timestamps
+// are int64 unix seconds.
+
+// RawMeasure is a network's native cumulative security measure: cumulative
+// hashes for PoW, stake-seconds for PoS.
+type RawMeasure struct {
+	Value string `json:"value"` // human-scaled mantissa (e.g. "484.44")
+	Unit  string `json:"unit"`  // e.g. "Zettahashes", "ETH·s"
+	Base  string `json:"base"`  // unscaled base amount (hashes or stake-seconds)
+}
+
+// SecurityResult is the security a single network accrued for a window/anchor,
+// exposed as the raw native measure AND a USD valuation (energy cost for PoW,
+// staked value for PoS), plus a normalized 0..1 score.
+type SecurityResult struct {
+	Network           string     `json:"network"`
+	Consensus         string     `json:"consensus"` // "pow" | "pos"
+	Raw               RawMeasure `json:"raw"`
+	ValueUSD          string     `json:"valueUsd"`          // decimal string
+	ValueUSDFormatted string     `json:"valueUsdFormatted"` // e.g. "$1,234.56"
+	Label             string     `json:"label"`             // e.g. "$X energy consumed" / "$X staked"
+	NormalizedScore   string     `json:"normalizedScore"`   // decimal string in [0,1]
+	SinceUnix         int64      `json:"since"`             // window/anchor start (unix seconds)
+	AsOfUnix          int64      `json:"asOf"`              // latest sample time (unix seconds)
+}
+
+// ReportAnchorInput is one anchor supplied in a report request. Provide either
+// Network ("BTC"/"ETH") or the public-chain numeric ChainID; Network wins.
+type ReportAnchorInput struct {
+	Network   string `json:"network,omitempty"`
+	ChainID   string `json:"chainId,omitempty"`
+	TxHash    string `json:"txHash"`
+	Timestamp int64  `json:"timestamp"` // anchor time, unix seconds
+}
+
+// ReportRequest is the body of ProofMeasure.Report: a transaction's interchain
+// anchors. The service computes the security each anchor's network accumulated
+// since the anchor and returns a TransactionReport.
+type ReportRequest struct {
+	TransactionID string              `json:"transactionId"`
+	PrimeID       string              `json:"primeId"`
+	BlockID       string              `json:"blockId"`
+	Anchors       []ReportAnchorInput `json:"anchors"`
+}
+
+// AnchorSecurity is one interchain anchor with the security its public network
+// has accumulated since the anchor was placed.
+type AnchorSecurity struct {
+	Network         string         `json:"network"`
+	AnchorTimestamp int64          `json:"anchorTimestamp"` // unix seconds
+	AnchorTxHash    string         `json:"anchorTxHash"`
+	Security        SecurityResult `json:"security"`
+}
+
+// HashPower is the combined raw hash power across a report's PoW anchors.
+type HashPower struct {
+	Value string `json:"value"`
+	Units string `json:"units"`
+}
+
+// TransactionReport is the per-transaction "securedBy" report: every public-chain
+// anchor covering the transaction's block with both raw and USD security, plus
+// combined totals. HashPower is nil when there are no PoW anchors.
+type TransactionReport struct {
+	TransactionID          string           `json:"transactionId"`
+	PrimeID                string           `json:"primeId"`
+	BlockID                string           `json:"blockId"`
+	Anchors                []AnchorSecurity `json:"anchors"`
+	TotalValueUSD          string           `json:"totalValueUsd"`
+	TotalValueUSDFormatted string           `json:"totalValueUsdFormatted"`
+	HashPower              *HashPower       `json:"hashPower"`
+	TotalNormalizedScore   string           `json:"totalNormalizedScore"`
+}
+
+// HealthResponse is the proof-measure liveness payload.
+type HealthResponse struct {
+	Status string `json:"status"`
+}