Guard os.listdir in PostProcessInterfaceDetailsList.parse() against missing dir and unrelated files

[Copilot]

PostProcessInterfaceDetailsList.parse() called os.listdir unconditionally, risking FileNotFoundError when no interfaces were generated and inadvertently opening unrelated files in the directory.

Changes

• Directory existence check — added os.path.isdir guard before os.listdir; logs a warning and returns early if the directory is absent
• File filtering — restricts iteration to files matching interface_*.{json,json.gz} (driven by self.compressed) plus an os.path.isfile guard to skip subdirectories
• Empty-set handling — warns and returns early when no matching interface files are found

Mirrors the pattern already established in CompileInterfaceSummaryJSON.parse().

if not os.path.isdir(self.path_interfaces):
    LOGGER.warning(...)
    return

ext = ".json.gz" if self.compressed else ".json"
interface_files = [
    f
    for f in os.listdir(self.path_interfaces)
    if f.startswith("interface_") and f.endswith(ext)
    and os.path.isfile(os.path.join(self.path_interfaces, f))
]

if not interface_files:
    LOGGER.warning(...)
    return