**Describe the bug**

blosc2_schunk_open_udio looks like it could be used to read an schunk from any seekable API (e.g. ftp), but it calls stat on the provided uri, requiring that the uri is known to the underlying OS filesystem API, which severely constrains where data can be source from. Providing any file is sufficient to trick this API into working, even if the file isn't a blosc2 compressed file. 

**To Reproduce**
TODO

**Expected behavior**
stat is not called, or stat is added as an optional callback in blosc2_io_cb

**Logs**
N/A

**System information:**
 - OS: Ubuntu 22.04
 - Compiler: clang
 - Version: fa5e3f4c5c645e315be0f998679b8e73b7d42680

**Additional context**
Add any other context about the problem here.
blosc2_schunk_open_udio calls stat
This is a GitHub Issue
repo:c-blosc2
owner:Blosc
Title : blosc2_schunk_open_udio calls stat
Issue date:

--- start body ---
**Describe the bug**

blosc2_schunk_open_udio looks like it could be used to read an schunk from any seekable API (e.g. ftp), but it calls stat on the provided uri, requiring that the uri is known to the underlying OS filesystem API, which severely constrains where data can be source from. Providing any file is sufficient to trick this API into working, even if the file isn't a blosc2 compressed file. 

**To Reproduce**
TODO

**Expected behavior**
stat is not called, or stat is added as an optional callback in blosc2_io_cb

**Logs**
N/A

**System information:**
 - OS: Ubuntu 22.04
 - Compiler: clang
 - Version: fa5e3f4c5c645e315be0f998679b8e73b7d42680

**Additional context**
Add any other context about the problem here.
--- end body ---

The blosc2_schunk_open_udio function in Blosc2 improperly relies on the stat system call, which restricts the function's ability to read from non-local sources (e.g., FTP). This could lead to potential security issues if an attacker can manipulate the URI to point to a malicious file, as the function does not validate the content type of the file being read. This could allow for unexpected behavior or exploitation if the function is used in a context where the integrity of the data is critical.