Add archive helpers and harden task runtime

site/doc/pages/gz_uncompress.txt

@@ -0,0 +1,22 @@
+:sig
+String gz_uncompress(String compressed)
+
+:params
+compressed : gzip-format compressed bytes
+return value : uncompressed bytes
+
+:see
+>sys
+gz_compress
+zip_list
+zip_extract
+
+:content
+Uncompresses a gzip-format byte string and returns the original content.
+
+```uce
+String compressed = file_get_contents("/tmp/hello.txt.gz");
+String plain = gz_uncompress(compressed);
+```
+
+`gz_uncompress()` validates the gzip header, CRC32 footer, and uncompressed-size footer. It throws a runtime error when the input is not a supported gzip stream or fails validation.