feat(prover-ray): preflight helpers

[ThomasPiellard]

Add a preflight hook to derive the shared randomness in the message bus compiler. The expected caller's sequence is now:

  // 1. declare MessageBus entries as part of normal constraint setup
  sys.NewMessageBusSend(ctx, originShard, handle, tab)
  sys.NewMessageBusReceive(ctx, originShard, handle, tab)

  // 2. wire the shared randomness before compiling
  messagebus.RegisterPreflightSeed(sys, sets, hasher)

  // 3. compile as usual
  messagebus.Compile(sys)
  grandproduct.Compile(sys)

latestUnreducedParticipantRound mirrors the logic of the existing
latestParticipantRound but works directly on sys.MessageBuses without
needing the pre-built byHandle map, so it can run before Compile has
grouped entries.

For the MSHash, the old prover's MSHash is used, and implements the following additive hash interface:

type MSetHash [MSetHashSize]field.Element

// Insert adds msg to the accumulator. Panics on an empty msg.
func (m *MSetHash) Insert(msg ...field.Element)

// Remove removes msg from the accumulator. Panics on an empty msg.
func (m *MSetHash) Remove(msg ...field.Element)

// Add combines two accumulators in place: m += other.
func (m *MSetHash) Add(other MSetHash)

[codecov]

Codecov Report

❌ Patch coverage is 30.12821% with 109 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...v/execution/ExecutionProofGeneratingCoordinator.kt	0.00%	92 Missing ⚠️
...ontract/l1/Web3JLinethRollupSmartContractClient.kt	34.78%	14 Missing and 1 partial ⚠️
...h/coordinator/config/v2/toml/ConfigLoaderHelper.kt	33.33%	2 Missing ⚠️

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