I am finally able to post the firmware, it has been rewritten in full assembly by @hidefromkgb and executes from RAM. As I expected, the device now consumes around 17-18 uA which means around 11 months of battery life, maybe even 12, since the previous firmware version lasted for 5 months instead of expected 4 months. However, I'm starting to have bigger plans for it. I realized that there is a lot of unused flash memory that can be used to log radioactivity data and display it via PC interface. Also check the drawing of a custom LCD that the final version may get:

There also will be a major update to the HV booster to get as much efficiency as possible with this form factor but it requires a custom transformer, and it will take some time to design and make. Two years of battery life is the new goal!