Log openat modes instead of every read / write

[krs85]

Right now we are intercepting every read and write. This is expensive and noisy. For now, let's instead log open calls by their mode. If a file is opened for reading only, we assume it's been read. If a file is opened with writing only, we assume it was written to. If it opens for both, we assume it was read and written.

• Remove read and write handling in event loop

• Stop intercepting read and write

• Extend handling of openat to report the mode the file is opened in

• move this logic to a helper function handle_openat()

• call this function in the posthook, not the prehook. The fd is not correct until the posthook, and we only want to report successful openings in read, write, or read/write mode, and successful file creations