requirements: add an official `REVLOG_COMPRESSION_ZSTD` const Such constant was missing and its value was missing from the set of requirements that needs to be preserved through stream clone. This did not had any consequence yet as the "bundle 2 does not filter its requirements" is shadowing the issue. However we are now in a situation where we can fix this issue. So lets do it next. With the preparation work on test, changing the streamreqs value only impact two tests, where checking the full value seems to remains relevant. Important note: Since older version of Mercurial used the old `supportedformat` class attribute to check for stream requirement they supported, older version will consider this requirements to prevent them from using streaming clone. Even as they support this requirements for years. Pack for stable will be send to fix it, but they will have to be backported to older version if needed. Differential Revision: https://phab.mercurial-scm.org/D12083