Remove TODO and move the compact-parts deviation into the number guide

Author: kipcole9

TODO.md

@@ -445,7 +445,9 @@ iex> Localize.Number.to_parts(1234567, format: :decimal_short)
  ]}
 ```
 
-The `:currency_long` formats and the RBNF rule-name formats do not decompose into parts and return an error from `to_parts/2`.
+The RBNF rule-name formats (`:spellout_cardinal` and friends) do not decompose into parts and return an error from `to_parts/2`.
+
+One known deviation from `Intl.NumberFormat.formatToParts`: the compact affix is a single `:compact` part including any adjoining space (`" million"`), where JS emits the space as a separate `:literal` part. Callers needing exact JS part boundaries can split leading/trailing whitespace off the `:compact` part.
 
 ### Rounding mode examples
 

guides/number_formatting.md

@@ -589,7 +589,7 @@ Units are organized into dimensional categories. Common categories and represent
 
 ## Custom units
 
-`Localize.Unit.define_unit/2` registers user-defined units at runtime via the `Localize.Unit.CustomRegistry`. Custom units participate in conversion, formatting, and arithmetic alongside built-in CLDR units.
+`Localize.Unit.define_unit/2` registers user-defined units at runtime via the `Localize.Unit.CustomRegistry`. Custom units participate in conversion, formatting, arithmetic, and parsing alongside built-in CLDR units. Hyphenated names ("double-cubit") are supported — a registered name matches wholesale before the unit grammar interprets hyphens as compound separators, just as CLDR's own hyphenated identifiers ("g-force", "kilowatt-hour") do.
 
 ### Linear custom units