fix(jsonrpc): report 256-bit integer fields in OpenRPC specification

Added 'UnsignedInteger256' schema for uint256 reference it in field 'Voucher.value'.
Updated these 'EvmAdvance' uint256 fields to reference 'UnsignedInteger256':
    - chain_id
    - block_number
    - block_timestamp
    - prev_randao
Kept 'EvmAdvance.index' and other genuine uint64 indexes on 'UnsignedInteger'.

Author: renatomaia

internal/jsonrpc/jsonrpc-discover.json

@@ -1956,7 +1956,7 @@
 				"type": "object",
 				"properties": {
 					"chain_id": {
-						"$ref": "#/components/schemas/UnsignedInteger"
+						"$ref": "#/components/schemas/UnsignedInteger256"
 					},
 					"application_contract": {
 						"$ref": "#/components/schemas/EthereumAddress"
@@ -1965,13 +1965,13 @@
 						"$ref": "#/components/schemas/EthereumAddress"
 					},
 					"block_number": {
-						"$ref": "#/components/schemas/UnsignedInteger"
+						"$ref": "#/components/schemas/UnsignedInteger256"
 					},
 					"block_timestamp": {
-						"$ref": "#/components/schemas/UnsignedInteger"
+						"$ref": "#/components/schemas/UnsignedInteger256"
 					},
 					"prev_randao": {
-						"$ref": "#/components/schemas/ByteArray"
+						"$ref": "#/components/schemas/UnsignedInteger256"
 					},
 					"index": {
 						"$ref": "#/components/schemas/UnsignedInteger"
@@ -2104,7 +2104,8 @@
 						"$ref": "#/components/schemas/EthereumAddress"
 					},
 					"value": {
-						"type": "string"
+						"$ref": "#/components/schemas/UnsignedInteger256",
+						"description": "Amount of Wei transferred by the voucher's call"
 					},
 					"payload": {
 						"$ref": "#/components/schemas/ByteArray"
@@ -2441,6 +2442,12 @@
 				"format": "hex-uint64",
 				"pattern": "^0x[a-fA-F0-9]{1,16}$"
 			},
+			"UnsignedInteger256": {
+				"type": "string",
+				"format": "hex-uint256",
+				"pattern": "^0x[a-fA-F0-9]{1,64}$",
+				"description": "256-bit unsigned integer, hex encoded (the node emits minimal hex)"
+			},
 			"FunctionSelector": {
 				"type": "string",
 				"format": "hex-byte",