rpc: graphql and otterscan clean-ups from the #23969 review

[AskAlexSharov]

Pre-existing items found in the review of #23969 (line numbers at its head acd1650). None changes behaviour on its own; each is a small separate fix.

• graphql map helpers are mostly dead. After rpc: return a typed struct from the receipt methods #23969, the map-based helpers in cmd/rpcdaemon/graphql/graph/helpers.go are only used for withdrawals, and the comment at helpers_test.go:69 still describes the old receipt flow.
• graphql fee fields duplicate ethapi.NewRPCTransaction. The type list at rpc/jsonrpc/graphql_api.go:77 repeats the type switch in ethapi.NewRPCTransaction, and the two already disagree for AccountAbstractionTxType: eth_getTransactionByHash shows the fee caps, graphql omits them.
• ots_getBlockTransactions marshals every receipt before cropping the page. At rpc/jsonrpc/otterscan_api.go:418, moving the pageEnd > len(receipts) check up and marshalling only receipts[pageStart:pageEnd] gives the same result.
• Lower-cased addresses pay for the EIP-55 checksum. strings.ToLower(addr.String()) at cmd/rpcdaemon/graphql/graph/resolver_helpers.go:190 (and for log and access-list addresses) computes the checksum and discards it; hexutil.Encode(addr[:]) gives the same string.

[VBulikov]

yperbasis added Imp2 as Importance