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

Pre-existing items found in the review of #23969 (line numbers at its head acd1650066). None changes behaviour on its own; each is a small separate fix.

- **graphql map helpers are mostly dead.** After #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.

Start with the locations named in the issue: cmd/rpcdaemon/graphql/graph/helpers.go and helpers_test.go, rpc/jsonrpc/graphql_api.go, rpc/jsonrpc/otterscan_api.go, and resolver_helpers.go. Read the related code and tests before separating the cleanup into a focused change. Done means the obsolete helper/comment, duplicated fee mapping, receipt pagination work, and lower-case address formatting each match the stated review findings without changing behavior.

Written by the indexing model from the issue text.