fix(pxe): support custom PrivateKernelProver and unify EmbeddedWalletOptions

[AztecBot]

Summary

• Fixes EmbeddedWallet silently ignoring custom PrivateKernelProver implementations passed via pxeOptions.proverOrOptions
• The instanceof BBPrivateKernelProver check in all three createPXE utils only matched BB's own prover subclasses — custom implementations fell through and were destructured as config options, causing runtime errors
• Replaced with a duck-type isPrivateKernelProver() guard using createChonkProof as the distinguishing method
• Unified the confusing pxeConfig/pxeOptions split in EmbeddedWalletOptions into a single pxe field that accepts both config and dependency overrides

New API

// Before (confusing — which one do I use?)
const wallet = await EmbeddedWallet.create(nodeUrl, {
  pxeConfig: { proverEnabled: true },
  pxeOptions: { proverOrOptions: myCustomProver },
});

// After (single unified option)
const wallet = await EmbeddedWallet.create(nodeUrl, {
  pxe: {
    proverEnabled: true,
    proverOrOptions: myCustomProver,
  },
});

The old pxeConfig/pxeOptions fields are kept but marked @deprecated.

Test plan

• Existing BB provers still pass the duck-type check (they implement createChonkProof)
• Plain BBPrivateKernelProverOptions objects correctly fall through to create default provers
• Custom PrivateKernelProver implementations are now correctly detected and used as-is
• Old pxeConfig/pxeOptions usage still works (backward compatible)
• New pxe field merges correctly with deprecated fields

[AztecBot]

❌ Failed to cherry-pick to v4-next due to conflicts. (🤖) View backport run.