Add method to get operator for distance

But why not centralize the logic? Each Vector Operator has an name, operator string, description, compatibility (e.g. Hamming and Jaccard work with binary vectors), etc.

To future-proof the package and make it flexible, it would be nice to centralize this logic. Moreover, in my particular case, I find myself needing to generate othe pgvector queries with dynamic operators and use the following:

    /**
     * @see https://github.com/pgvector/pgvector-php/pull/12
     */
    protected function tempGetDistanceOperator(): string
    {
        return match ($this->distance) {
            Distance::L2 => '<->',
            Distance::InnerProduct => '<#>',
            Distance::Cosine => '<=>',
            Distance::L1 => '<+>',
            Distance::Hamming => '<~>',
            Distance::Jaccard => '<%>',
            default => throw new \InvalidArgumentException('Invalid distance')
        };
    }

which fits, in my view, into the enum.

Thank you for considering my comment.

P.S. This is my first ever pull request. :)

pgvector / pgvector-php

Add method to get operator for distance #12