refactor: replace embd_normalize integer parameter with enum

[SaurabhCodes-16]

Overview

This PR refactors the embedding normalization parameter from a plain int to a strongly typed enum common_embd_norm, addressing the inline TODO comment in common/common.h.

Specifically:

• Defined enum common_embd_norm representing the normalization types (-1=none, 0=max absolute, 1=taxicab, 2=euclidean).
• Refactored common_embd_normalize signature and all parsing, server, and example client usages.
• Added a performance optimization for the L1 Taxicab norm (COMMON_EMBD_NORM_TAXICAB) avoiding unnecessary std::pow calls.

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: YES - Assisted by Antigravity AI coding assistant to refactor parameter signatures/definitions to the new enum and implement the L1 norm optimization.