feat(DrumDisplay): optional leading-zero suppression for variable-width readouts

[mottihoresh]

Motivation

Some readouts show a variable number of digits with no leading zeros — e.g. the AN/ARC-51A preset-channel window (#171) displays 1..9 as a single digit and 10..20 as two. Today DrumDisplay always renders the full nDigits width, so a 2-digit readout would show 01 instead of 1.

Proposal

Add a per-readout option to DrumReadout:

• bool suppressLeadingZero — default false (no behavior change for existing readouts: APN-153 speed, ASN-41 nav digits, etc.).
• When true: blank the high-order digit cells until the first non-zero digit. The remaining digits still roll/animate normally (animation unchanged).

Scope

• suppressLeadingZero field on DrumReadout (default false).
• Render path: blank leading-zero cells when enabled; keep tape animation for the live digits.
• Unit test: 1↔2 digit transition (e.g. 9→10→9) renders without a leading zero; default-false path unchanged.

Consumers

• ARC-51 (AN/ARC-51A UHF Radio Control Panel #171) channel window — opt-in true. ARC-51 B1 is blocked on this for the channel readout.

Out of scope

Render-mode / snap-vs-animate (animation stays as-is per maintainer). This ticket is leading-zero only.