Remove deprecated ESLint rules and husky.sh lines

[Mimori256]

This PR removes deprecated configurations uncovered during dependency updates (#671).

changes:

• Remove deprecated ESLint rule @typescript-eslint/camelcase
  • This rule was already disabled, so this change has no functional impact
• Remove the deprecated ESLint rule space-before-function-paren
  • Prettier already enforces function spacing, so this rule should be redundant.
• Remove deprecated husky.sh lines (ref: https://github.com/typicode/husky/releases/tag/v9.1.1)

• Remove npm exec from .husky/pre-commit
  • npm exec is no longer required since v9.1.1 and removing it slightly improves performance according to the release note

Now husky shows this message when commiting so that deprecated husky.sh lines should be removed:

husky - DEPRECATED

Please remove the following two lines from .husky/pre-commit:

#!/usr/bin/env sh
. "$(dirname -- "$0")/_/husky.sh"

They WILL FAIL in v10.0.0