Forward MSP_ELRS_BACKPACK_SET_DVR_NAME to the goggles

[bob9]

Summary

Adds a new MSP_ELRS_BACKPACK_SET_DVR_NAME (0x030F) message carrying a race label the goggles use to name the next DVR recording (companion to the hdzero-goggle dvr-race-names feature).

• The VRX backpack forwards the packet verbatim over the goggle serial link via a new MSPModuleBase::ForwardPacket.
• ModuleBase::ForwardPacket is an empty stub, so non-MSP backpack modules (rapidfire, rx5808, etc.) ignore the message — same dispatch pattern as SetOSD/SetRecordingState.

Additive only: 21 lines, no changes to existing message handling.

Related PRs

• Send RTC time from the TX backpack to the VRX backpack over ESP-NOW #231 — sends RTC time from the TX backpack to the VRX backpack over ESP-NOW, so DVR recordings named by this feature also get correct timestamps. Both PRs were split out of Send RTC time and DVR recording name from the TX backpack to the goggles #230.
• Automatically sync backpack time from the handset (real timestamps on goggle DVR) + lua memory optimisations Lua-Scripts#18 — adds a Sync Backpack Time button to the ELRS Lua script that seeds the TX backpack clock from the handset.
• Race timer sets DVR filenames to the heat you flew, e.g. hdz_0042-WinterCup-Mains-A-R5-H1.mp4 hd-zero/hdzero-goggle#613 — companion goggle PR: handles MSP_SET_DVR_NAME and names the next DVR recording with the received label.
• Let pilots switch between Raceband and Lowband via the ELRS backpack hd-zero/hdzero-goggle#614 — same race-timer integration: lets the timer also switch the goggles between Raceband and Lowband (independent of this PR).