BREAKING: Mark All Integers Safe & Tighten Schema

[bachmacintosh]

Description

This PR marks as many known integers as a SafeInteger type as possible, going beyond just parameter arguments; this will help make the values more reusable should we make further adjustments to the type, such as branding it.

We also used this PR as an opportunity to change any v.union([type, v.null()]) items to simply v.nullable(type) for brevity; this may be a breaking change for any consumers relying on the issue structure when parsing fails. We also found a couple zod schema that weren't using z.toZod when they should've.

Nature of Pull Request

This Pull Request:

• Adds/Updates Type(s)/Schemas
• Adds/Updates Helper Functions/Type Guards
• Updates Documentation
• Updates Project and/or Community Health files (e.g. README, GitHub Actions, etc.)

Its changes constitutes a:

• Non-code change (i.e. no version bump)
• Bug Fix or Other Small Changes (i.e. patch version bump)
• Forward-compatible Enhancement (i.e. minor version bump)
• ⚠️ BREAKING CHANGE regarding TypeScript, Package, and/or WaniKani API version(s) (i.e. MAJOR version bump)

Contribution Terms

I understand that by submitting this Pull Request:

• I agree to the terms outlined in the Contribution Guidelines and Code of Conduct
• My code will be licensed for use in this repository per its LICENSE, and that I have the right to license this code -- per GitHub's Terms of Service

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
packages/types/src/v20170710/base.ts	100.00% <ø> (ø)
...s/types/src/v20170710/spaced-repetition-systems.ts	100.00% <ø> (ø)
packages/types/src/v20170710/user.ts	100.00% <ø> (ø)
packages/valibot/src/v20170710/assignments.ts	100.00% <ø> (ø)
packages/valibot/src/v20170710/base.ts	100.00% <ø> (ø)
...ckages/valibot/src/v20170710/level-progressions.ts	100.00% <ø> (ø)
packages/valibot/src/v20170710/resets.ts	100.00% <ø> (ø)
...ackages/valibot/src/v20170710/review-statistics.ts	100.00% <ø> (ø)
packages/valibot/src/v20170710/reviews.ts	100.00% <ø> (ø)
...valibot/src/v20170710/spaced-repetition-systems.ts	100.00% <ø> (ø)
... and 17 more

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