feat(units): read back every form the drawing writes

The readout learned to write lengths as 5'-6 1/2" and angles as
N 45d0'0" E, but typed input was still a bare parse::<f64>() — a
coordinate could be displayed and not entered. Give the formatters
their inverses.

parse_length takes feet and inches separated by a dash, a space, or
nothing, with the closing quote optional, and whole-plus-fraction in
any of those forms: 5', 60", 5'-9", 5'9-1/2, 9-1/2, 1/2. A leading
minus is a sign; the one inside 5'-9" is a separator, since after feet
there is nothing left to subtract from.

parse_angle reads the mark that says which convention an angle is in —
g for grads, r for radians, d/'/" for degrees-minutes-seconds, compass
letters for a surveyor's bearing — and reads a bare number in whichever
convention the drawing is set to.

ANGBASE and ANGDIR now apply, but only where they mean something. Which
way a thing points is measured from the drawing's zero and runs the way
it says; how wide an arc opens is the same number whatever zero is
counted from. format_direction and parse_direction are the pair for
directions, and the polar readout and polar input both go through them,
so the bearing shown is the bearing accepted. format_angle stays for
sizes, where applying a base angle would corrupt the value.

The command prompts follow the same rule, each classified rather than
swept: OFFSET distance, FILLET radius, CHAMFER distances, ARRAY and
MINSERT spacing, TRACE width, HELIX, and EXTRUDE height read lengths;
the four dimension text-rotation prompts, ARRAY's total angle and
INSERT's rotation read angles. MLINE's scale and INSERT's scale factor
are left alone — a multiplier has no unit to be written in. INSERT read
both through one parse; they are now separate.

The typed variants also take a decimal comma, which a single-value
prompt has no other use for. parse_length itself does not: inside a
coordinate the comma separates the axes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/modules/insert/solid3d_cmds.rs

@@ -77,9 +77,7 @@ impl CadCommand for ExtrudeCommand {
         self.step == ExtrudeStep::Height
     }
     fn on_text_input(&mut self, text: &str) -> Option<CmdResult> {
-        text.trim()
-            .parse::<f64>()
-            .ok()
+        crate::entities::common::parse_typed_length(text)
             .filter(|&h| h.abs() > 1e-6)
             .map(|h| CmdResult::ExtrudeEntity {
                 handle: self.target_handle,