feat: normalize Plutus V4 backend handling

[wolf31o2]

Summary

• Decode and hydrate Plutus V4 reference scripts across shared, Blockfrost, Maestro, and Ogmios paths.
• Normalize Plutus V4 cost models and compute V4 script-data language views.
• Reject V4 witness/reference-script construction clearly until Apollo adds Dijkstra transaction support.

Tests

• go test -race ./...
• go test -race ./backend/...

[Copilot]

Pull request overview

This PR extends Apollo v2’s Plutus support to recognize and normalize Plutus V4 across backends (protocol params + reference scripts), while explicitly rejecting constructing Conway-era transactions that would require Dijkstra-era Plutus V4 witness/reference-script support.

Changes:

• Added Plutus V4 language-view support in ComputeScriptDataHash and expanded ScriptRef decoding/creation paths to understand PlutusV4.
• Normalized backend protocol-parameter cost model parsing/mapping to include "PlutusV4" (UTxO RPC, Ogmios/Kupo, Maestro, Blockfrost) and added V4 reference-script decoding.
• Introduced explicit builder-level rejection (ErrPlutusV4RequiresDijkstra) for attaching/using Plutus V4 scripts in Conway-era transaction construction, with targeted tests.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
helpers.go	Adds PlutusV4 cost-model language mapping and ScriptRef type detection for V4.
helpers_test.go	Adds script-data-hash language-view test coverage for PlutusV4.
backend/utxorpc/utxorpc.go	Refactors cost-model parsing and adds PlutusV4 extraction from RPC protocol params.
backend/utxorpc/utxorpc_test.go	Tests that RPC cost-model translation includes PlutusV4.
backend/ogmios/ogmios.go	Extends Ogmios cost-model key mapping and reference-script decoding to PlutusV4; adds Kupo language constant shim.
backend/ogmios/ogmios_test.go	Adds tests for PlutusV4 script-ref decoding and cost-model key translation.
backend/maestro/maestro.go	Extends Maestro cost-model key mapping and script-ref decoding to PlutusV4.
backend/maestro/maestro_test.go	Adds tests for Maestro PlutusV4 script-ref and cost-model key translation.
backend/blockfrost/blockfrost.go	Extends script language detection-from-hash to include PlutusV4.
backend/blockfrost/blockfrost_test.go	Adds PlutusV4 cost-model parsing and script-ref detection test coverage.
backend/base.go	Adds ScriptRefFromBytes support for ScriptRefTypePlutusV4.
backend/base_test.go	Adds ScriptRefFromBytes PlutusV4 test coverage.
apollo.go	Adds ErrPlutusV4RequiresDijkstra and rejects PlutusV4 witness/reference-script construction paths.
apollo_test.go	Adds tests for V4 rejection behavior and V4 ScriptRef construction behavior.

Comments suppressed due to low confidence (1)

helpers.go:604

• NewScriptRef only matches non-pointer Plutus script types and uses hard-coded numeric type tags (0..4). This makes it easy to reject valid *common.PlutusVxScript values and risks drifting from common.ScriptRefType* constants used elsewhere (e.g. backend/base.go:309+). Consider accepting pointer forms and using the shared constants for the ref type codes.

func NewScriptRef(script common.Script) (*common.ScriptRef, error) {
	var scriptType uint
	switch script.(type) {
	case common.NativeScript:
		scriptType = 0
	case common.PlutusV1Script:

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