Add a Rosetta method spec and import it into the cosmos bundle

[BabyScope]

What this adds

Rosetta is a POST-only HTTP API that a cosmos operator runs beside the node — cosmos/rosetta, since the SDK dropped its in-process implementation in v0.50. Its paths are already expressible in the existing spec format (POST#/block, POST#/network/status), but no spec declares them, so nodecore cannot route to a Rosetta sidecar at all.

This PR adds pkg/methods/specs/rosetta.json — a plain spec on the rest-additional connector covering the Data API, the Construction API and /search/transactions — and imports it into the cosmos bundle. It is modelled directly on the existing hyperliquid-rest-additional.json.

   "spec-imports": [
     "cosmos-tendermint",
     "cosmos-rest",
-    "cosmos-grpc"
+    "cosmos-grpc",
+    "rosetta"
   ]

Why rest-additional

Rosetta is a separate service on its own port, not a namespace on the node, which is exactly what rest-additional is described as in data.go: "used for connectors that provide extra REST methods, but they can't be used for chain-specific". It also keeps the change inert for everyone else:

• an operator opts in per upstream by adding a rest-additional connector pointing at their Rosetta URL;
• upstreams without one are unaffected, since a method is only dispatchable on a connector the upstream declares;
• IsAdditionalApiConnectorType excludes it from head and internal-request connector selection, so it can never become an upstream's head connector.

Verification

Run against an Axelar mainnet archive (axelar-dojo-1, earliest_block_height 1), on an upstream with a tendermint connector for the head and a rest-additional connector for Rosetta:

POST /queries/<chain>/network/status
  -> {"current_block_identifier":{"index":34661178,...},
      "genesis_block_identifier":{"index":1,...}}

POST /queries/<chain>/network/list
  -> {"network_identifiers":[{"blockchain":"app","network":"network"}]}

Historical blocks through the same upstream, ~0.11 s per call:

block	result
1	ok, 1 tx
100 000	ok, 1 tx
5 000 000	ok, 2 txs
15 000 000	ok, 2 txs
25 000 000	ok, 1 tx
30 000 000	ok, 1 tx
34 000 000	ok, 1 tx

The tendermint methods on that same upstream keep answering unchanged (status → axelar-dojo-1), and an undeclared path still fails cleanly with the method POST#/... does not exist/is not available.

Note for reviewers

The one-line edit to cosmos.json could not be exercised locally, because NewMethodSpecLoaderWithExtraFs adds specs rather than overriding them and rejects a duplicate name. The runs above used a bundle with the same import pattern and this exact rosetta.json; only the bundle's name differs.

Happy to split the spec out of the cosmos bundle and leave it standalone if you would rather have chains opt in explicitly, or to extend it to other chain families.