Handle checks with letters better in phase/check mode

[bulatb]

Running yuno run check m-n won't find tests in checks between m and n if they have lettered subparts like check<m+1>a. They're still reachable through run <glob>, but it would be better if the phase and check syntax supported them.

It should work like this:

• check 6 or check 6a - Exactly match check6/ or check6a/
• check 6-10 - Match any checks between 6 and 10, inclusive, and including every sub-check.
• check 6a-c - Match checks 6a, 6b, and 6c
• check 6b-19a - Match as above, but starting at 6a and going through 15, 15a, 15b, and 19 to 19a. Subchecks in the range should be matched as greedily as possible.