Add GetRace

[benrobey]

Step 4: GetRace

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You can now fetch one race directly by its id.

How it works:

• New RPC GetRace(id) returns the race or a NOT_FOUND error.
• Status field (OPEN/CLOSED) is still derived at read time, just like in the list.
• Follows AIP-131 conventions

Example: get race 1

curl -s localhost:8000/v1/races/1 

Response:

{
	"id": "1",
	"meetingId": "5",
	"name": "North Dakota foes",
	"number": "2",
	"visible": false,
	"advertisedStartTime": "2021-03-03T01:30:57Z",
	"status": "RACE_STATUS_CLOSED"
}