add 'ignored_commands' option to stats

[drmorr0]

This resolves #1714.

I add a ignored_commands option to stats so that common commands that you don't want showing up in stats can be skipped.

• I am unsure what the default for this option should be: I left it empty so as to keep it consistent with existing behaviour. Happy to change that if you want.
• I added a test for this, which required updating the return signature for compute_stats -- I think in the long run the way to test this is by splitting out compute_stats from the function that prints the results, but I thought that might be too much for this PR. Happy to take a stab at this if you disagree.

Output on my machine, using ignored_commands = ["cd", "vi", "ls"]:

(before)

> target/release/atuin stats
[▮▮▮▮▮▮▮▮▮▮] 903 cd
[▮▮▮▮▮▮▮▮▮ ] 874 vi
[▮▮▮▮▮▮    ] 619 ls
[▮▮        ] 199 kcgp
[▮         ] 166 git stat
[▮         ] 159 kcl
[▮         ] 141 kcapp
[▮         ] 131 kcrm
[▮         ] 131 git co
[▮         ] 119 kcg
Total commands:   6747
Unique commands:  1933

(after)

> target/release/atuin stats
[▮▮▮▮▮▮▮▮▮▮] 199 kcgp
[▮▮▮▮▮▮▮▮  ] 166 git stat
[▮▮▮▮▮▮▮   ] 159 kcl
[▮▮▮▮▮▮▮   ] 141 kcapp
[▮▮▮▮▮▮    ] 131 git co
[▮▮▮▮▮▮    ] 131 kcrm
[▮▮▮▮▮     ] 119 kcg
[▮▮▮▮▮     ] 110 kns
[▮▮▮▮▮     ] 109 git amend
[▮▮▮▮▮     ] 107 rm
Total commands:   4352
Unique commands:  1457

Checks

• I am happy for maintainers to push small adjustments to this PR, to speed up the review cycle
• I have checked that there are no existing pull requests for the same thing

[ellie]

lgtm! thanks