More sophisticated pty size: account for horizontal space taken by timestamp
============================================================================
Currently, when a program outputs a full-sized progress bar (assuming #1 is fixed, which I have locally), this is what we get, visually:
```
% ets wget 'https://devstreaming-cdn.apple.com/videos/wwdc/2020/10114/3/E2A04285-0BB5-42D7-9BD6-643A
0DD51EC7/wwdc2020_10114_hd.mp4'
[2020-07-01 13:52:19] --2020-07-01 13:52:19-- https://devstreaming-cdn.apple.com/videos/wwdc/2020/1
0114/3/E2A04285-0BB5-42D7-9BD6-643A0DD51EC7/wwdc2020_10114_hd.mp4
[2020-07-01 13:52:19] Resolving devstreaming-cdn.apple.com (devstreaming-cdn.apple.com)... 17.253.97
.204, 17.253.15.208
[2020-07-01 13:52:19] Connecting to devstreaming-cdn.apple.com (devstreaming-cdn.apple.com)|17.253.9
7.204|:443... connected.
[2020-07-01 13:52:19] HTTP request sent, awaiting response... 200 OK
[2020-07-01 13:52:19] Length: 124443527 (119M) [video/mp4]
[2020-07-01 13:52:19] Saving to: ‘wwdc2020_10114_hd.mp4’
[2020-07-01 13:52:19]
[2020-07-01 13:52:19]
[2020-07-01 13:52:19] wwdc2020_10114_hd.mp4 0%[ ] 0 --
[2020-07-01 13:52:20] wwdc2020_10114_hd.mp4 21%[======> ] 25.17M 1
[2020-07-01 13:52:20] wwdc2020_10114_hd.mp4 46%[===============> ] 55.40M 1
[2020-07-01 13:52:20] wwdc2020_10114_hd.mp4 77%[==========================> ] 91.68M 1
[2020-07-01 13:52:20] wwdc2020_10114_hd.mp4 100%[==================================>] 118.68M 1
59MB/s in 0.7s
[2020-07-01 13:52:20]
[2020-07-01 13:52:20] 2020-07-01 13:52:20 (159 MB/s) - ‘wwdc2020_10114_hd.mp4’ saved [124443527/1244
43527]
[2020-07-01 13:52:20]
```
The problem is that the pty inherits the entire width of the tty when a portion is taken up by the timestamp. The fix is that we should virtually render a timestamp, then deduct that width from the tty's width.