Document language for dates; @eval pathname resolution and :cwd (from dev bc7cd62b6f68)

@date/@datetime gain :lang (German: "16. Juni 1910") over a document-wide
Language state variable, and :number for the numeric form (en 6/16/1910,
de 16.06.1910 per DIN 5008).  @eval finds Python modules next to the file
that names them regardless of the cwd, and the new :cwd option runs an
eval in a chosen working directory (@source_file uses it to resolve
against the document).  Two new test suites ship in tst/.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

sks/code/code.k

@@ -12,7 +12,9 @@ A word or phrase displayed verbatim in a line
 @@c :: @eval code_format.Code_fragment(K) eval@
 @@
 
-@@source_file filename : @eval code_format.Source(K) @ @@
+# :cwd makes the filename resolve against the DOCUMENT's directory, not
+# the directory ktext happens to run in.
+@@source_file filename : @eval :cwd *K_input_dir* code_format.Source(K) @ @@
 
 
 #[