Request: avoid adding extensions to filepaths which already contain them.

[lukethehuman]

When using blobmaker in an optimisation workflow, we already need to track the majority of filepaths. Thus, it's more straightforward to pass the full filepath directly to methods such as GeometryMaker.export_exodus. However, currently this causes filenames with two extensions like so: filename.e.e. This can be avoided by removing the extension when passing to such methods, but it would be preferable if blobmaker could check for the extension before adding it.

Consider the following code block to achieve this:

from pathlib import Path

# Get required extension, e.g. for exodus:
ext = ".e"

# Add required extension if it is not already present.
filepath = Path(filepath)  # Ensure path is a pathlib.Path object
if filepath.suffix != ext:  # Check for extension
    filepath = filepath.parent / (filepath.name + ext)  # Add the extension

# If you need the filepath as a string again, just pass it like so:
str(filepath)

As shown, pathlib makes it quite easy to check the file extension (or suffix) and is a built-in module for python so doesn't require adding a dependency.