volt: beam: Q82 -- json_canonical.py says it is not JCS and names the three measured divergences

- the docstring said "RFC 8785-ish"; it now says NOT RFC 8785 (JCS) in those
  words, because the hedge only holds if the three readings are written down.
- measured at this file (scratch/q82/floats.py, output in the closure record):
  -0.0 -> "-0.0" where RFC 8785 Table 1 gives "0"; 1e-06 -> "1e-06" where the
  table gives "0.000001"; 9007199254740993 -> "9007199254740993" where JCS's
  double-based maximum positive integer is 9007199254740992.
- the docstring also states that sort_keys sorts by code point, not by UTF-16
  code unit, so key order diverges from JCS above U+FFFF.
- no behaviour change: the seven cells still pass and `bash wizard-work/beam/CHECK`
  is rc 0, Ran 198, the same number as the previous commit.

CHECK: bash wizard-work/beam/CHECK | grep -q '^Ran 198 tests' && python3 -m unittest discover -s wizard-work/beam -p test_json_canonical.py

wizard-work/beam/json_canonical.py

@@ -1,5 +1,17 @@
-"""Canonical JSON serialization (RFC 8785-ish): sorted keys, compact separators,
+"""Canonical JSON serialization: sorted keys, compact separators, no NaN/Infinity,
-no NaN/Infinity, deterministic float repr, UTF-8, ensure_ascii=False."""
+deterministic float repr, UTF-8, ensure_ascii=False.
+
+NOT RFC 8785 (JCS), and not claimed to be. JCS is IEEE-754 double-based with its
+own number grammar; this module emits Python's `repr` for floats and passes int
+through unchanged. Three measured divergences from RFC 8785 Table 1:
+
+    -0.0    -> "-0.0"                (JCS: "0")
+    1e-06   -> "1e-06"               (JCS: "0.000001")
+    2**53+1 -> "9007199254740993"    (JCS max positive integer: 9007199254740992)
+
+Key order is `sort_keys=True`, i.e. by Unicode code point; JCS sorts by UTF-16
+code unit, so the two diverge above U+FFFF.
+"""
 from __future__ import annotations
 import json
 import math