Improve hash control precision

[mourner]

It always slightly annoyed me that the hash control isn't very precise — e.g. if you navigate to a certain place, then open a new tab and copy the url, it will be slightly off, with a bigger error the more you zoom in. So I derived a new formula for the hash that makes it always precise while keeping the low number of digits on lower zoom levels.

Here's a table with a comparison of the number of digits after the decimal point:

z	old	new
z0	0	1
z1	0	1
z2	1	2
z3	2	2
z4	2	2
z5	3	2
z6	3	3
z7	3	3
z8	3	3
z9	4	4
z10	4	4
z11	4	4
z12	4	5
z13	4	5
z14	4	5
z15	4	5
z16	4	6
z17	5	6
z18	5	6
z19	5	7
z20	5	7
z21	5	7
z22	5	8

The calculation is derived from the following formula:

512px * 2^zoom / 360 / 10^numDigits < 0.5px

Launch Checklist

• briefly describe the changes in this PR
• write tests for all new functionality
• manually test the debug page

[anandthakker]

Nice! The new formula makes more sense, too 👍