Audio broken after silence in rerendered video

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## Description of bug / unexpected behavior
When having audio after silence, that audio is broken in rerendered videos.
Meanwhile the audio before the silence stays fine.

```py
class AudioTest(Scene):
def construct(self):
# audio before silence works fine
self.add_sound("audio.wav")
self.wait(5)
# silence
self.wait(3)
# audio after silence is broken after rerender
self.add_sound("audio.wav")
self.wait(5)
```

This bug seems to be caused by the caching system since the audio is fine
* for the initial render
* when disabling the caching

For example when looking at the following videos, you can see (hear) that when there is some silence at the start, the rerendered video doesn't have any audio. (first row)

Initial Render
Rerender
Rerender without caching

## Expected behavior
The audio after the silence should work in the rerendered video.

## How to reproduce the issue

Code for reproducing the problem

```py
from manim import *
import soundfile as sf

class InitialSilenceTest(Scene):
def construct(self) -> None:
# some silence
self.wait(3)
# playing a sound
self.add_sound("audio.wav")
self.wait(sf.info("audio.wav").duration)

class MiddleSilenceTest(Scene):
def construct(self) -> None:
self.add(Text("Middle Silence"))
self.add_sound("audio.wav")
self.wait(sf.info("audio.wav").duration)
self.wait(3)
self.add_sound("audio.wav")
self.wait(sf.info("audio.wav").duration)

class NoSilenceTest(Scene):
def construct(self) -> None:
self.add(Text("No Silence"))
self.add_sound("audio.wav")
self.wait(sf.info("audio.wav").duration)
```

I used these commands to videos above.
```console
manim main.py InitialSilenceTest MiddleSilenceTest NoSilenceTest

manim main.py InitialSilenceTest -o InitialSilenceTestRerendered
manim main.py MiddleSilenceTest -o MiddleSilenceTestRerendered
manim main.py NoSilenceTest -o NoSilenceTestRerendered

manim main.py InitialSilenceTest --disable_caching -o InitialSilenceTestNoCaching
manim main.py MiddleSilenceTest --disable_caching -o MiddleSilenceTestNoCaching
manim main.py NoSilenceTest --disable_caching -o NoSilenceTestNoCaching
```

## Additional media files

Audio

[audio.wav](https://github.com/user-attachments/files/28403222/audio.wav)

Start by running the provided InitialSilenceTest, MiddleSilenceTest, and NoSilenceTest commands, comparing the initial render, cached rerender, and --disable_caching results. Trace the caching and audio-rendering paths involved in rerendering; done means audio after silence is present and correct in cached rerenders as well as uncached renders.

Written by the indexing model from the issue text.