feat: define Int8

[hargoniX]

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[leanprover-community-bot]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 76164b284b0769672d8a643c4396356a6f053fba --onto 8151ac79d66e7990d5bf5e1b71f8a33aec7d6446. (2024-10-22 09:54:49)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 76164b284b0769672d8a643c4396356a6f053fba --onto 66dbad911eaaec4cd512662bd5cc67a2a16d2484. (2024-10-23 10:21:30)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 76164b284b0769672d8a643c4396356a6f053fba --onto 09e1a05ee922bf8581ba9820f096ac1a2b1a2945. (2024-10-24 15:05:10)