docs: describe Int and Float bounds 🤖 (#357)

[frobel0520]

Summary

• Document the min and max bounds accepted by Int and Float.
• Describe the default bounds and effective constructor options.

Closes #357

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.19%. Comparing base (5b398be) to head (0df1276).

Components	Coverage Δ
traitlets	85.60% <ø> (ø)
tests	99.07% <ø> (ø)

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