feat: optimize fresh device conversation sync

[redflyingfish]

🅰 Please add the issue ID after "Fixes #"

Fixes #3496
Depends on openimsdk/protocol#203.

Summary

This PR optimizes fresh device conversation sync for users with a large number of conversations.

When a fresh device logs in with idHash = 0, the server currently returns all owner conversation IDs. For users with many historical conversations, this can produce a very large sync response and trigger expensive follow-up sync work.

This change:

• adds optional pagination support to GetFullOwnerConversationIDs;
• returns the total number of filtered conversation IDs;
• filters read and inactive conversations only when the conversation count is above the threshold;
• keeps pinned conversations in the full sync result;
• adds a dedicated full-sync seq RPC path so ordinary seq queries do not fetch userMinSeq;
• adds tests for pagination, hash matching, pinned conversations, inactive filtering, cleared conversations, and small conversation sets.

Protocol dependency

This PR requires the protocol additions from openimsdk/protocol#203:

• GetFullOwnerConversationIDsReq.pagination
• GetFullOwnerConversationIDsResp.total
• GetConversationsFullSyncSeqs
• FullSyncSeqs.userMinSeq

Until openimsdk/protocol#203 is merged and released, CI builds that use the current official protocol version may fail with missing GetConversationsFullSyncSeqs types/methods.

After the protocol PR is merged and released, this PR should bump github.com/openimsdk/protocol to the corresponding version.

Testing

Tested locally with github.com/openimsdk/protocol replaced by the protocol branch from openimsdk/protocol#203:

go test -mod=mod ./internal/rpc/conversation ./internal/rpc/msg ./pkg/rpcli ./pkg/common/storage/controller ./pkg/common/storage/model

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[redflyingfish]

Hi maintainers, the CLA Assistant link currently returns 404 for me, so I cannot complete the CLA signature from the provided link. Could you please check the CLA configuration or provide the correct signing URL?

Also, the current CI failure is expected because this server PR depends on openimsdk/protocol#203, and the official protocol version used by main does not include the new GetConversationsFullSyncSeqs generated types yet.