Error location annotations don't line up when _hs source uses tabs for indentation

hyperscript's error annotations (the `^^` markers) do not line up with the printed source when it uses tab characters as indentation:

When spaces are used in the source, the marker lines up correctly:

This issue is because, when the annotation creator ([`createParserContext`](https://github.com/bigskysoftware/_hyperscript/blob/455a32d30533c198cdf9a75a053c41520de04249/src/_hyperscript.js#L1311)) is figuring out where to place the marker, it counts tab characters as a single character. If, on the first example, the tab characters are replaces with single spaces, the marker lines up correctly:

To solve this, either:
- Around `createParserContext`'s call to `String.repeat`, tabs would be specially-cased for the offset to count as some number of characters (4, 8, ...) rather than just one.
- Or, the whitespace before the true start of a line could be copied, where the marker offset will only counted from the "real" start of the line (iow, where the indentation ends), and afterwards the saved whitespace is prepended to the `" ".repeat(offset)`, something like
```diff
diff --git a/tmp/1 b/tmp/2
index c054964..a688d74 100644
--- a/tmp/1
+++ b/tmp/2
@@ -4,7 +4,8 @@
var lines = source.split("\n");
var line = currentToken && currentToken.line ? currentToken.line - 1 : lines.length - 1;
var contextLine = lines[line];
+ var leadingWhitespace = contextLine.match(/^\s+/)[0];
var offset = /** @type {number} */ (
currentToken && currentToken.line ? currentToken.column : contextLine.length - 1);
- return contextLine + "\n" + " ".repeat(offset) + "^^\n\n";
+ return contextLine + "\n" + leadingWhitespace + " ".repeat(offset - leadingWhitespace.length) + "^^\n\n";
}
```
This is of course a bit hacky and doesn't take into account things like tabs in the middle of a line (which solution no.1 would do correctly, and only that among other edge cases I'm not smart enough to think of), but it works fine!

Even with mixed indentation!

---

Using:
- _hyperscript 0.9.14, (originally from unpkg)
- Firefox 141.0.3
- Debian 13 `Linux 6.12.38+deb13-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.38-1 (2025-07-16) x86_64 GNU/Linux`

src/_hyperscript.js の createParserContext から開始し、タブインデント、混在インデント、スペースインデントの _hs ソースでアノテーション出力を再現します。マーカーのオフセットがどのように計算されるかを追跡し、それぞれの場合に、結果の ^^ マーカーが報告されたソース位置と一致することを確認します。

索引モデルが issue の本文から書いたものです。