chore(cli): Improve validation for kill and run commands

[irvinlim]

1. Standardize to use Complete(), Validate(), Run() functions.
2. Add validation for time in the past in --after and --at for the run command.
3. Standardize -t and -p shorthand flags from kill to run also.
4. Fix some typos in error messages.

[codecov[bot]]

Codecov Report

Base: 69.48% // Head: 69.56% // Increases project coverage by +0.08% :tada:

Coverage data is based on head (bb49327) compared to base (5119dba). Patch coverage: 78.04% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #122 +/- ## ========================================== + Coverage 69.48% 69.56% +0.08% ========================================== Files 192 192 Lines 9765 9781 +16 ========================================== + Hits 6785 6804 +19 + Misses 2615 2613 -2 + Partials 365 364 -1 ``` | [Impacted Files](https://codecov.io/gh/furiko-io/furiko/pull/122?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=furiko-io) | Coverage Δ | | |---|---|---| | [pkg/cli/cmd/cmd\_kill.go](https://codecov.io/gh/furiko-io/furiko/pull/122?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=furiko-io#diff-cGtnL2NsaS9jbWQvY21kX2tpbGwuZ28=) | `80.43% <74.28%> (+7.01%)` | :arrow_up: | | [pkg/cli/cmd/cmd\_run.go](https://codecov.io/gh/furiko-io/furiko/pull/122?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=furiko-io#diff-cGtnL2NsaS9jbWQvY21kX3J1bi5nbw==) | `80.25% <100.00%> (+0.25%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=furiko-io). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=furiko-io)

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