Use printf escape tokens for ESC and BEL

[qstrahl]

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Don't ask me why, but without using the printf shorthand for these escape sequences, I was getting all kinds of garbage text printed in each new window, among other rendering weirdness. In theory, there should be no difference between using these shorthand tokens and using the numeric literals, but this fixed the issue for me so... ¯\_(ツ)_/¯

For reference, my versions (though I didn't test on others):

❯ fish --version ; tmux -V
fish, version 3.0.2
tmux 2.9a

[tomyun]

Sorry for such a long delay! I didn't get any notification from this repo and totally forgot about it. With that, I'm not sure why/whether this issue still happens, i.e., on recent versions of fish/tmux. Let me know if you have any updates.