fix(explore): Ensure variadic field and environment flags are arrays

[sentry]

This PR addresses CLI-2B4, a TypeError: e.find is not a function occurring in the sentry explore command.

The root cause was that Stricli's variadic: true flags (specifically --field and --environment in the explore command) return a plain string when only a single value is provided, instead of a single-element array. This led to a TypeError when array methods like .find() were called on these flags.

The fix normalizes flags.field and flags.environment to arrays using ([] as string[]).concat(flag_value) immediately after they are parsed. This ensures that subsequent code always operates on an array, regardless of whether one or multiple values were provided by the user.

Fixes CLI-2B4

_{Comment @sentry <feedback> on this PR to have Autofix iterate on the changes.}

[github-actions]

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[github-actions]

Codecov Results 📊

✅ Patch coverage is 100.00%. Project has 5494 uncovered lines.
✅ Project coverage is 81.75%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
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+ Coverage    81.75%    81.75%        —%
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  Files          428       428         —
  Lines        30106     30108        +2
  Branches     19593     19597        +4
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+ Hits         24611     24614        +3
- Misses        5495      5494        -1
- Partials      2054      2056        +2

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