Reference pages for the rest of std, and Part III sections on them

Pages for (std eq), (std clr-ord), (std monad), (std effect),
(std hashset), (std orderedset), (std orderedmap), (std inbox),
(std ports), (std net), (std test), (std simpletest), (std stopwatch)
and (std syntax-match), and for the five (std mutable ...) modules in
a directory of their own, as (std stm) has. Part III has a short
section on each group with links to its pages.

🤖 Generated with [ECA](https://eca.dev) (anthropic/claude-opus-5-5)

Co-Authored-By: eca-agent <git@eca.dev>

modules/std/hashset.sz

@@ -0,0 +1,3 @@
+(meta (title "(std hashset)"))
+
+@generate-docs[#:module "std hashset"]