fix: matplotlib SyntaxError in sandboxed Pyodide code execution (#26800)

The sandboxed Pyodide host (used when ENABLE_PYODIDE_FILE_PERSISTENCE is
disabled, the default) embeds its script in a String.raw template. The
matplotlib show() override was written with '\\t' escapes as if in a normal
string context, but String.raw preserves them verbatim, so the iframe's
script parser turns them into literal backslash-t characters in the
generated Python source. Pyodide then fails to compile any code that
triggers the matplotlib patch with "SyntaxError: unexpected character
after line continuation character", which is why matplotlib only worked
with the file persistence worker path enabled.

Use single '\t' escapes instead: String.raw keeps them as-is in the
script text and the sandbox's JS parser produces real tab indentation,
matching the working implementation in pyodide.worker.ts.

Fixes #26660

src/lib/pyodide/pyodideSandboxHost.ts

@@ -116,13 +116,14 @@ const sandboxScript = String.raw`
 			'_old_show = matplotlib.pyplot.show',
 			'assert _old_show, "matplotlib.pyplot.show"',
 			'def show(*, block=None):',
-			'\\tbuf = BytesIO()',
-			'\\tmatplotlib.pyplot.savefig(buf, format="png")',
-			'\\tbuf.seek(0)',
-			'\\timg_str = base64.b64encode(buf.read()).decode("utf-8")',
-			'\\tmatplotlib.pyplot.clf()',
-			'\\tbuf.close()',
-			'\\tprint(f"data:image/png;base64,{img_str}")',
+			// String.raw keeps \t as-is; the sandbox's JS parser turns it into a real tab
+			'\tbuf = BytesIO()',
+			'\tmatplotlib.pyplot.savefig(buf, format="png")',
+			'\tbuf.seek(0)',
+			'\timg_str = base64.b64encode(buf.read()).decode("utf-8")',
+			'\tmatplotlib.pyplot.clf()',
+			'\tbuf.close()',
+			'\tprint(f"data:image/png;base64,{img_str}")',
 			'matplotlib.pyplot.show = show'
 		].join('\n'));
 	}