examples: migrate to the native data layer (drop ws/coder-websocket/jackson/jsonlite) (#316)

Stacked on #315 (the native Binance REST fetcher). Retarget to `main` once #315 merges.

Migrates the runnable examples off third-party data-I/O packages onto Wickra's
native data layer (`CandleReader`, `Resampler`, `BinanceFeed`, `fetch_*klines`).

## Third-party packages removed (the zero-dep selling point)
- **Node**: `ws` (live feed → BinanceFeed) — dropped from package.json + lockfile
- **Go**: `github.com/coder/websocket` — dropped from go.mod / go.sum (`go mod tidy`)
- **Java**: `jackson-databind` (live feed + REST fetch) — dropped from pom.xml
- **R**: `jsonlite` + `websocket` + `later` — dropped from the README notes

Each language's CSV loading now goes through `CandleReader`, manual resampling
through `Resampler`, the live feed through `BinanceFeed`, and (Java/R) the REST
download through the native fetcher.

## Verification
Ran the offline examples per language against the bundled data — backtest and
multi_timeframe produce identical output across Python / Node / Go / Java / R
(e.g. ATR(14) last 345.1010; 1h→5m resamples to 240 bars, →15m to 80 bars).

C# / C / WASM (stdlib-only, no third-party deps to remove) follow in this branch.

Note: the streaming `strategy_*` examples have pre-existing candle-indicator
runtime bugs (CI only syntax-smokes them); the CSV migration preserves their
shape and leaves those bugs for a separate fix.

examples/go/live_binance/main.go

@@ -1,54 +1,42 @@
 // Stream live BTCUSDT 1-minute klines from Binance and feed each close through EMA(20).
-// Requires network access (build-only in CI). Runs for up to 60 seconds.
+// Uses Wickra's native BinanceFeed — no third-party WebSocket client. Requires
+// network access (build-only in CI). Runs for up to 60 seconds.
 package main
 
 import (
-	"context"
-	"encoding/json"
 	"fmt"
 	"log"
-	"strconv"
 	"time"
 
-	"github.com/coder/websocket"
 	wickra "github.com/wickra-lib/wickra/bindings/go"
 )
 
 func main() {
-	const url = "wss://stream.binance.com:9443/ws/btcusdt@kline_1m"
-	fmt.Printf("Connecting to %s (up to 60s)...\n", url)
+	fmt.Println("Streaming live BTCUSDT 1-minute klines from Binance (up to 60s)...")
 
-	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
-	defer cancel()
-
-	conn, _, err := websocket.Dial(ctx, url, nil)
+	// Native feed: a blocking poll over the same tested stream as the Rust core.
+	feed, err := wickra.NewBinanceFeed("BTCUSDT", wickra.OneMinute, "")
 	if err != nil {
-		log.Fatalf("dial: %v", err)
+		log.Fatalf("connect: %v", err)
 	}
-	defer conn.CloseNow()
+	defer feed.Close()
 
 	ema, _ := wickra.NewEma(20)
 	defer ema.Close()
 
-	for {
-		_, data, err := conn.Read(ctx)
+	deadline := time.Now().Add(60 * time.Second)
+	for time.Now().Before(deadline) {
+		// next() returns the event and ok=true, ok=false on timeout (poll again),
+		// or an error once the stream is closed.
+		event, ok, err := feed.Next(time.Second)
 		if err != nil {
-			fmt.Println("Done (time limit reached).")
+			fmt.Println("Done (feed closed).")
 			return
 		}
-
-		var msg struct {
-			K struct {
-				Close string `json:"c"`
-			} `json:"k"`
-		}
-		if err := json.Unmarshal(data, &msg); err != nil || msg.K.Close == "" {
+		if !ok {
 			continue
 		}
-		closePx, err := strconv.ParseFloat(msg.K.Close, 64)
-		if err != nil {
-			continue
-		}
-		fmt.Printf("close=%.2f  EMA(20)=%.2f\n", closePx, ema.Update(closePx))
+		fmt.Printf("close=%.2f  EMA(20)=%.2f\n", event.Close, ema.Update(event.Close))
 	}
+	fmt.Println("Done (time limit reached).")
 }