refactor(server-ng): remove use server::* imports from core/server-ng

[jaya-traversal]

`core/server-ng` imports several utilities from `core/server`, the legacy binary it is meant to replace. This creates a compile-time dependency that prevents server-ng from ever building independently.

The imports fall into five clusters across `main.rs`, `bootstrap.rs`, and `server_error.rs`:

File	Import
`main.rs`	`server::bootstrap::create_shard_executor`
`main.rs`	`server::diagnostics::print_*_info` (3 fns)
`main.rs`	`server::log::logger::Logging`
`bootstrap.rs`	`server::bootstrap::create_directories`
`bootstrap.rs`	`server::log::logger::Logging`
`bootstrap.rs`	`server::streaming::partitions::storage::{load_consumer_group_offsets, load_consumer_offsets}`
`bootstrap.rs`	`server::streaming::segments::storage::create_segment_storage`
`bootstrap.rs`	`server::bootstrap::load_segments`
`server_error.rs`	`server::server_error::LogError`

Each cluster is independently removable with no behaviour change. The storage and partition log clusters depend on #3298 landing first, since that PR moves the relevant types out of `core/server`.

[hubcio]

@numinnex what we're doing with this one?

[numinnex]

Hi, the dependency on the server crate in server-ng is temporarely there due to code reuse of some core mechanism such as segment loading or consumer offset loading. We wanted to get rid of them together when we replace server binary with the server-ng one, but if you have an idea how to improve state of the affairs in a quick way, we are down to merge it.

[jayakasadev]

Thanks for the context, @numinnex.

A PR is coming shortly that cleans up main.rs entirely — it moves create_shard_executor and the io_uring diagnostics into a new core/server-runtime crate shared by both core/server and core/server-ng. No behaviour change.

bootstrap.rs and server_error.rs still have remaining use server::* imports. The storage/partition loading ones (load_segments, create_segment_storage, load_consumer_offsets) need #3298 to land first since that PR moves those types out of core/server. The rest (create_directories, Logging, LogError, ShardAllocator) can follow in separate PRs after Phase 1 merges.

PR: #3331