[improvement](fe) Support framed blocking Thrift servers

[Yukang-Lian]

What problem does this PR solve?

Issue Number: close #xxx

Related PR: None

Problem Summary:

Custom FE server starters may need a blocking server transport while retaining the framed wire protocol used by threaded-selector clients. Previously, ThriftServer built its thread-pool server inline and only supported the unframed transport, so extensions had to duplicate Doris worker-pool construction to preserve the framed protocol.

This change adds a shared thread-pool server factory with an explicit framed-transport option. The existing unframed production path now uses the same factory. A focused end-to-end test verifies both framed and unframed RPC round trips.

Release note

Support constructing framed thread-pool Thrift servers for custom FE server starters.

Check List (For Author)

• Test
  • Unit Test
  • Regression test
  • Manual test
  • No need to test or manual test
• Behavior changed:
  • No.
  • Yes. Custom server starters can opt into framed transport on a blocking Thrift server.
• Does this need documentation?
  • No.
  • Yes.

Validation: ./run-fe-ut.sh --run org.apache.doris.common.ThriftServerTest (2 tests passed).

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1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
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4. Which code was refactored and why was this part of the code refactored?
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