Support FFmpeg 7.0 (#48)

* sys: Run cargo fmt

* sys: Add new channel layout consts

* sys: Update build script for 7.0

- Add new FF_API flags
- Update version_check_info range
- Add ffmpeg_7_0 feature entry

* sys: Update non-exhaustive match statement

* Update enums

* Mark old APIs as removed with 7.0

* Make Audio frame work with 7.0

The .unwrap() in clone() is a bit wonky

* Add API for swr_alloc_set_opts2

* Use AVFrame::duration field in 7.0+

* Include 7.0 in CI runs

* Add fn ChanneLayoutIter::best

* Update examples for new API

* Add/update Context setter for ch layout

examples/codec-info.rs

@@ -47,7 +47,8 @@ fn main() {
                     println!("\t formats: any");
                 }
 
-                if let Some(layouts) = audio.channel_layouts() {
+                #[cfg(feature = "ffmpeg_5_1")]
+                if let Some(layouts) = audio.ch_layouts() {
                     println!("\t channel_layouts: {:?}", layouts.collect::<Vec<_>>());
                 } else {
                     println!("\t channel_layouts: any");
@@ -97,7 +98,8 @@ fn main() {
                     println!("\t formats: any");
                 }
 
-                if let Some(layouts) = audio.channel_layouts() {
+                #[cfg(feature = "ffmpeg_5_1")]
+                if let Some(layouts) = audio.ch_layouts() {
                     println!("\t channel_layouts: {:?}", layouts.collect::<Vec<_>>());
                 } else {
                     println!("\t channel_layouts: any");