Add function to revoke permit on BPT

[EndymionJkb]

Description

Per ToB issue:
"The BalancerPoolToken contract implements the permit function, allowing users to sign a payload in order to allow another user or contract to spend their tokens. However, once a user signs a payload and sends it to another user, they have no way of revoking this signature. Since only one nonce is valid until it is consumed, this would prevent the original user from submitting permit signatures with a different nonce."

This adds a revokePermit function that increments the nonce.

Type of change

• Bug fix
• New feature
• Breaking change
• Dependency changes
• Code refactor / cleanup
• Optimization: [ ] gas / [ ] bytecode
• Documentation or wording changes
• Other

Checklist:

• The diff is legible and has no extraneous changes
• Complex code has been commented, including external interfaces
• Tests have 100% code coverage
• The base branch is either main, or there's a description of how to merge

Issue Resolution

Resolves #1007