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/csharp/_common/MarketData.cs

@@ -45,34 +45,17 @@ public static class MarketData
     /// </summary>
     public static Bar[] LoadOhlcvCsv(string path)
     {
-        var bars = new List<Bar>();
-        foreach (var rawLine in File.ReadLines(path))
+        // Native CandleReader: header validation, BOM and field-whitespace tolerance.
+        // No manual CSV parsing.
+        using var reader = new Wickra.CandleReader(File.ReadAllText(path));
+        var candles = reader.Read();
+        var bars = new Bar[candles.Length];
+        for (var i = 0; i < candles.Length; i++)
         {
-            var line = rawLine.Trim();
-            if (line.Length == 0)
-            {
-                continue;
-            }
-
-            var cols = line.Split(',');
-            if (!double.TryParse(cols[0], System.Globalization.CultureInfo.InvariantCulture, out _) &&
-                !long.TryParse(cols[0], out _))
-            {
-                continue; // header row
-            }
-
-            double F(int i) => double.Parse(cols[i], System.Globalization.CultureInfo.InvariantCulture);
-
-            if (cols.Length >= 6)
-            {
-                bars.Add(new Bar(F(1), F(2), F(3), F(4), F(5), long.Parse(cols[0])));
-            }
-            else
-            {
-                bars.Add(new Bar(F(0), F(1), F(2), F(3), F(4), bars.Count));
-            }
+            var c = candles[i];
+            bars[i] = new Bar(c.Open, c.High, c.Low, c.Close, c.Volume, (long)c.Timestamp);
         }
 
-        return bars.ToArray();
+        return bars;
     }
 }