chore: update dependency casbin to ^5.51.1

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
casbin (source)	^5.50.0 → ^5.51.1

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Release Notes

apache/casbin-node-casbin (casbin)

v5.51.1

Compare Source

Bug Fixes

• use tsup for ESM build to resolve ERR_UNSUPPORTED_DIR_IMPORT (2d90c7d)

v5.51.0

Compare Source

Features

• add exports field to package.json for ESM-only environments (b9a5fc6)

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