remote: Add zstd to encoding types

Allows us to skip gzip compression when uploading .zst files.
Includes adding ".zst" to the mimetypes encoding types dictionary
because it is not yet included in the standard library.¹

¹ https://github.com/python/cpython/blob/2ef3676a5bb8fba531fb8237ce50c27ebe37fb96/Lib/mimetypes.py#L411-L417

nextstrain/cli/remote/s3.py

@@ -65,6 +65,9 @@
 mimetypes.add_type("application/json", ".json")
 mimetypes.add_type("text/markdown", ".md")
 
+# Add zstd to encodings map since it is not yet included in the standard library
+mimetypes.encodings_map[".zst"] = "zstd"
+
 
 def upload(url: urllib.parse.ParseResult, local_files: List[Path], dry_run: bool = False) -> Iterable[Tuple[Path, str]]:
     """
@@ -281,6 +284,9 @@ def guess_type(path: Path) -> Tuple[str, Optional[str]]:
     >>> guess_type(Path("metadata.tsv.xz"))
     ('text/tab-separated-values', 'application/x-xz')
 
+    >>> guess_type(Path("metadata.tsv.zst"))
+    ('text/tab-separated-values', 'application/zstd')
+
     >>> guess_type(Path("metadata.tsv.Z"))
     ('text/tab-separated-values', 'application/octet-stream')
 
@@ -292,6 +298,7 @@ def guess_type(path: Path) -> Tuple[str, Optional[str]]:
         "gzip": "application/gzip",
         "xz": "application/x-xz",
         "bzip2": "application/x-bzip2",
+        "zstd": "application/zstd",
     }
 
     type, encoding = mimetypes.guess_type(path.name)