[feature] support processing of (many) more media types (#3090)

* initial work replacing our media decoding / encoding pipeline with ffprobe + ffmpeg

* specify the video codec to use when generating static image from emoji

* update go-storage library (fixes incompatibility after updating go-iotools)

* maintain image aspect ratio when generating a thumbnail for it

* update readme to show go-ffmpreg

* fix a bunch of media tests, move filesize checking to callers of media manager for more flexibility

* remove extra debug from error message

* fix up incorrect function signatures

* update PutFile to just use regular file copy, as changes are file is on separate partition

* fix remaining tests, remove some unneeded tests now we're working with ffmpeg/ffprobe

* update more tests, add more code comments

* add utilities to generate processed emoji / media outputs

* fix remaining tests

* add test for opus media file, add license header to utility cmds

* limit the number of concurrently available ffmpeg / ffprobe instances

* reduce number of instances

* further reduce number of instances

* fix envparsing test with configuration variables

* update docs and configuration with new media-{local,remote}-max-size variables

vendor/codeberg.org/gruf/go-iotools/size.go

@@ -0,0 +1,25 @@
+package iotools
+
+type Sizer interface {
+	Size() int64
+}
+
+// SizerFunc is a function signature which allows
+// a function to implement the Sizer type.
+type SizerFunc func() int64
+
+func (s SizerFunc) Size() int64 {
+	return s()
+}
+
+type Lengther interface {
+	Len() int
+}
+
+// LengthFunc is a function signature which allows
+// a function to implement the Lengther type.
+type LengthFunc func() int
+
+func (l LengthFunc) Len() int {
+	return l()
+}