Version 2.5.0, refactoring with breaking changes, requires Varnish 6.5.1

- Faster implementations of .match() and .hasprefix()
- .compile() is now required in vcl_init
- Various methods may invoke VCL failure on unrecoverable errors.
- Some means have been added to safeguard against VCL failure.
- Added the 'element' parameter, sets may now be used as associative arrays.
- For details see in the source repository.
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