…on (#21646)

## Summary

`--chain dev` couldn't produce blocks past genesis. Two bugs, plus a
builder cleanup found while addressing review:

- **Beacon API routes not registered** — dev mode set
`BeaconAPIRouter.Active=true` but never enabled endpoint groups
(`Beacon`, `Node`, `Validator`, `Config`, `Events`). The embedded dev
validator polls `/eth/v1/beacon/genesis` which returned 404, deadlocking
block production.

- **CL/EL fork mismatch: Prague/Osaka not activated, system contracts
missing** — the CL ran Fulu (epoch 0) but the EL had `PragueTime=nil`
and `OsakaTime=nil`. Pre-Prague EL headers carry no `requestsHash`,
while the CL reconstructs the header with `SHA256("")` = `e3b0c442…`
over the (empty) execution-requests list, so every produced block was
rejected with "mismatching hash" (`cl/cltypes/eth1_block.go`).
Activating Prague in turn requires the system-contract predeploys in the
dev genesis alloc.

- **Dead `requestsHash` override in the builder removed** —
`execution/builder/exec.go` re-derived `header.RequestsHash` after
`AssembleBlock`, but on a discarded header copy: the final block is
rebuilt from `current.Header` in `finishBlock`, which
`merge.FinalizeAndAssemble` already stamps with `outRequests.Hash()`
(`empty.RequestsHash` for empty request sets). An earlier revision of
this PR changed the dead write from `common.Hash{}` to
`empty.RequestsHash`; it is now deleted outright, leaving
`FinalizeAndAssemble` as the single source of truth. Verified dead by
running the new regression test against the old zero-hash code (passes)
and against zero-hash corruption injected into the live `merge.go` path
(fails with "invalid block hash").

The dev genesis is now a faithful Cancun+Prague genesis and lives in the
genesis layer:

- All five system contracts are predeployed via `allocs/dev.json`
(copied verbatim from `allocs/hoodi.json`): EIP-6110 deposit contract
(with `DepositContract` set in the chain config — fixes the
`ParseDepositLogs` WARN on every block), EIP-4788 beacon roots
(otherwise a silent no-op with Cancun at genesis), EIP-2935 history
storage, EIP-7002 withdrawal requests, EIP-7251 consolidation requests.
- Fork times (Shanghai/Cancun/Prague/Osaka at 0), TTD=0 and the deposit
contract address moved from `SetEthConfig` into
`DeveloperGenesisBlock()`; the remaining Caplin/beacon-genesis setup is
extracted into `setDevnetEthConfig`, leaving the `SetEthConfig` switch
case at one line.
- `TestEngineApiBuiltBlockEmptyRequestsHash` pins the requests hash of
an empty-request Prague block end to end (FCU → getPayload → newPayload
→ canonical header via RPC).

Dev mode now runs full Fusaka: Fulu on CL, Osaka on EL.

Note: the dev genesis hash changes (new predeploys in the alloc) — wipe
existing `--chain dev` datadirs.

## Test plan

- [x] `erigon --chain dev --dev.slot-time 2` produces Fulu/Osaka blocks
at 2s intervals
- [x] Transactions confirmed on-chain (ETH transfers, contract
deployment)
- [x] No `ParseDepositLogs` WARNs; EIP-4788 ring buffer populated
(`eth_getStorageAt` of slot `timestamp % 8191` returns the block
timestamp); block `requestsHash` is `e3b0c442…`
- [x] `TestEngineApiBuiltBlockEmptyRequestsHash` fails on injected
live-path corruption, passes otherwise
- [ ] CI passes

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: yperbasis <andrey.ashikhmin@gmail.com>