fix(iso): use hvc1 sample entry for H.265 fMP4

[modeitsch]

Summary

• write H.265 fMP4 video sample entries as hvc1 instead of hev1
• keep ISO parsing compatible with existing hev1 entries while adding hvc1 support
• add regression coverage for H.265 sample entry generation and decoding

Root cause

go2rtc advertises H.265 MSE streams with an hvc1 codec string, but the fMP4 init segment was written with an hev1 sample entry. Some browsers reject that mismatch when creating or appending to the MSE SourceBuffer.

Validation

• GOCACHE=/private/tmp/go-build-cache GOPATH=/private/tmp/go-path go test ./pkg/iso

Fixes #2205