opencv-rust compatability

[Rust's opencv bindings](https://github.com/twistedfall/opencv-rust) used to just work with rusty_ffmpeg, but switching from 0.14 to 0.15 breaks linking.

Adding this line to any Cargo.toml using `rusty_ffmpeg` v0.15+ causes this issue:
```toml
opencv = { version = "0.93.1", default-features = false, features = ["clang-runtime"] }
```

```
/usr/bin/ld: /workspaces/myproject/ffmpeg/./libavutil/timestamp.h:76: undefined reference to `av_ts_make_time_string2'
/usr/bin/ld: /workspaces/myproject/ffmpeg/./libavutil/timestamp.h:76: undefined reference to `av_ts_make_time_string2'
/usr/bin/ld: /workspaces/myproject/ffmpeg/./libavutil/timestamp.h:76: undefined reference to `av_ts_make_time_string2'
/usr/bin/ld: /workspaces/myproject/ffmpeg/./libavutil/timestamp.h:76: undefined reference to `av_ts_make_time_string2'
```

Tested with FFmpeg 7.0 and 7.1