bug: IndexError when an exec block shares a page with a large `:::` mkdocstrings directive

Hi!

I ran into a build failure I'm fairly sure comes from markdown-exec.

I have a reference page with one python exec="true" block near the top
and :::tsecon.x13._spec lower down. The submodule documents about 87 symbols.
With both on the same page, mkdocs build dies with:

File ".../markdown_exec/_internal/processors.py", line 105, in run
  markup: Markup = self.md.htmlStash.rawHtmlBlocks[counter]
IndexError: list index out of range

Either one alone is fine. It only breaks in combination.

I spent a while bisecting and the failure seems to track the number of
stashed HTML blocks mkdocstrings emits, not anything specific in any one
docstring (spot-removing individual docstrings doesn't help; the failure
just shifts around). Threshold seems to be somewhere around 80 stashed
blocks.

Bisection, all with the same exec block on the page:

Smallest repro I have:

# Title

```python exec="true" source="material-block"
print("hi")
```

::: package_with_many_symbols

For now I dropped exec="true" on that one page and shipped the
quick-start as plain python; the rest of the docs build fine. I'm just
reporting this so it's on your radar. I would be happy to put together
a stripped-down reproducer if that would help.

(markdown-exec 1.12.1, mkdocstrings python handler current, mkdocs-material current.)

Thanks for markdown-exec, by the way, we use it across our whole
tutorial corpus.

Best!