math.nim: Use func everywhere (#16285)

* math.nim: procs with {.noSideEffect} -> funcs

* math.nim: procs without {.noSideEffect.} -> funcs

* math.nim: proc -> func in links

* math.nim: proc -> func in doc comments

* test: add `math` to strictFuncs test

tests/effects/tstrict_funcs.nim

@@ -2,7 +2,15 @@ discard """
   cmd: "nim c --experimental:strictFuncs --experimental:views $file"
 """
 
-import tables, streams, nre, parsecsv, uri, httpcore, strutils
+import tables, streams, parsecsv
+# We import the below modules to check that they compile with `strictFuncs`.
+# They are otherwise unused in this file.
+import
+  httpcore,
+  math,
+  nre,
+  strutils,
+  uri
 
 type
   Contig2Reads = TableRef[string, seq[string]]