server: panic on non-numeric filenames in consumer offset directories

[atharvalade]

When loading consumer offsets at startup, the server panics if any file in the consumer offset directory has a non-numeric filename.

File: core/server/src/streaming/partitions/storage.rs lines 183-186, 247-252

let name = dir_entry.file_name().into_string().unwrap();
let consumer_id = name.parse::<u32>().unwrap_or_else(|_| {
    panic!("Invalid consumer ID file with name: '{}'.", name);
});

An operator accidentally placing a file (e.g. .DS_Store, editor swap file, backup) in the consumer offsets directory crashes the server on startup. This should be a warning + skip, not a panic.

I think we should log a warning and skip non-numeric filenames instead of panicking.

[atharvalade]

Please assign this to me

[hubcio]

remember that at this point test is more important than the implementation. code in core/server (single node) will get replaced by core/server-ng which will have support for cluster. don't modify server-ng though, we will do it later on.

we don't want the bugs to carry over. at some point in the future, when we will start the migration, we will run all existing tests on new binary.