beacon/engine, rpc: add PremarshaledJSON for execution payload envelopes

[jrhea]

Adds a PremarshaledJSON fast path for ExecutionPayloadEnvelope that bypasses encoding/json's reflection and re-validation, which are expensive for large payloads with many blobs.

goos: darwin
goarch: arm64
pkg: github.com/ethereum/go-ethereum/eth/catalyst
cpu: Apple M4 Max
BenchmarkGetPayloadV5WithBlobs/blobs=21/enc=none-16                                   10         101667408 ns/op               101.5 ms/op      12892132 B/op       4355 allocs/op
BenchmarkGetPayloadV5WithBlobs/blobs=21/enc=json-16                                    8         131135370 ns/op               131.0 ms/op      37107522 B/op       7197 allocs/op
BenchmarkGetPayloadV5WithBlobs/blobs=21/enc=json_premarshaled-16                      10         106992271 ns/op               106.9 ms/op      18620180 B/op      4403 allocs/op
BenchmarkGetPayloadV5WithBlobs/blobs=21/enc=rlp-16                                    10         104075679 ns/op               104.0 ms/op      29606241 B/op      4378 allocs/op
BenchmarkGetPayloadV5WithBlobs/blobs=72/enc=none-16                                   10         101948704 ns/op               101.8 ms/op      44432680 B/op     12788 allocs/op
BenchmarkGetPayloadV5WithBlobs/blobs=72/enc=json-16                                    6         174747340 ns/op               174.7 ms/op      143662510 B/op    22277 allocs/op
BenchmarkGetPayloadV5WithBlobs/blobs=72/enc=json_premarshaled-16                      10         115809462 ns/op               115.7 ms/op      64227073 B/op     12810 allocs/op
BenchmarkGetPayloadV5WithBlobs/blobs=72/enc=rlp-16                                    10         108373650 ns/op               108.3 ms/op      106355096 B/op    12806 allocs/op

Note: This PR uses @MariusVanDerWijden's benchmarks from #33944. I will rebase when his PR gets merged.

TODO Maybe?:

The PremarshaledJSON method in premarshal.go is currently hand-written. If ExecutionPayloadEnvelope changes, the code must be updated manually. To make this sustainable, gencodec could be extended to emit PremarshaledJSON() alongside MarshalJSON().