Change Speed effect no longer sample accurate

### Bug description

In previous versions of Audacity, entering "New Length" in the Change Speed effect would give sample accurate results.
In 3.2.0 (release version), the new length may be slightly wrong.

### Steps to reproduce

1) Open audacity
2) Click generate menu -> generate chirp
3) Set duration to 2 minutes exactly (00h 02m 00s + 00000 samples)
4) Click 'generate' button
5) Double-click audio region to ensure length is 00h 02m 00s + 00000 samples (might need to change your display settings to see samples)
6) Click Effect->Change Speed
7) Set new duration to 00h 03m 00s + 00000 samples (might need to change your display settings to see samples)
8) Click 'Apply' button
9) Double-click audio region to see length
10) note that length is 00h 02m 59s + 44060 samples, not 00h 03m 00s + 00000 samples
11) @Paul-Licameli : observe also, when you open Change Speed again, that the new duration setting is not retained to
sample precision.

### Expected behavior

The stretched length should be exactly 00h 03m 00s + 00000 samples

### Actual behavior

The stretched length is 00h 02m 59s + 44060 samples

### Audacity Version

latest stable version (from audacityteam.org/download)

### Operating system

Linux

### Additional context

Reported on macOS. Confirmed on Linux.

Although it's not off by much, it's enough to mess up critical work such as synchronising sound with video, or synchronising recording made with multiple recorders.