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/kutil/kutil.k

@@ -80,3 +80,17 @@ An <id> is the value of the ^:id argument for an image.
   :pattern [\s\S]*
   :python_cast (lambda s: __import__("kutil").filename_list(s))
 @@@
+
+@@@argtype language |
+  an ISO 639-1 language code (two lowercase letters) selecting the language
+  of text a klammer generates, e.g. en (English) or de (German).  The
+  languages actually available are listed by the klammer that uses the
+  argument (^@date and ^@datetime); an unknown code reports them.
+  :pattern [a-z][a-z]
+@@@
+
+# The document-wide language for generated text.  A klammer's own :lang
+# argument overrides it; see the language argtype above.  Consumers today:
+# @date and @datetime (month names and date form).  Set it for a whole
+# document with  @@@state Language :value de @@@
+@@@state Language :desc Language (ISO 639-1) for generated text :value en @@@