[v1.30.0] Backport Network API changes to `v1.x` branch

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Description Meilisearch v1.30.x introduces breaking changes to sharding / network behavior that currently impact all SDKs.

SDKs appear to assume pre-1.30 behavior and do not yet fully account for the new leader-based cluster model, asynchronous topology changes, and updated /network semantics.

1. Removal of sharding flag from /network

   • The previous sharding: true configuration is no longer supported.
   • Cluster behavior is now controlled via:
     • self
     • remotes
     • leader

2. Leader-only write operations

   • When a leader is configured:
     • Many write routes fail with not_a_leader if executed on a non-leader node e.g. index creation / deletion /document addition / deletion etc.

Other For a complete list of breaking changes you can read List of changes section in v1.30.0