[MattieGit]

Summary

• async_get_software_version() returns None when register 77 reads 0, instead of "0.00".
• The register is not populated on some firmware: it reads 0 on two Qubes (4.1.00 and another unit in its own VLAN), so Home Assistant showed software version "0.00" whenever the mDNS lookup was unavailable. None leaves the version empty, which is honest.
• Non-zero values are formatted as before. A unit on 4.1.01 was reported to read 4101 here; converting that to "4.1.01" is left out until the value is confirmed.
• Version 1.16.1.

Testing

• New test: a register reading 0 returns None. Existing tests unchanged; 142 pass, ruff 0.14.14 clean.
• Not verified live: the Qube accepts one Modbus client, which Home Assistant holds.

Hold: do not release until the open core PRs are merged (core pins 1.16.0).