[Pipe] Add receiver session authentication integration tests

[Caideyipi]

Description

Add integration-test coverage for the pipe receiver authentication and session changes in #17741, #18111, and commit e32465e2 (#18084).

Legacy pipe receiver

• Verify legacy handshake, file transfer, and pipe-data RPCs require login and USE_PIPE.
• Verify deletion and TsFile loading use the authenticated user's permissions.
• Verify handshake and TsFile loading do not auto-create databases or schema when auto creation is disabled.

DataNode and ConfigNode receivers

• Verify V1 handshakes are rejected and V2 handshakes validate credentials.
• Verify unauthenticated requests are rejected while authenticated client sessions remain usable.
• Verify successful DataNode receiver handshakes establish a session that can transfer tablets.

Two-stage aggregation

• Verify count-point-processor uses the source username and password for its internal two-stage aggregate sender.
• Run the source and result sink in separate 1C1D clusters and assert the combined count is transferred successfully.

Verification

• mvn clean package -DskipTests -Drat.skip=true -pl integration-test -am -P with-integration-tests
• IoTDBLegacyPipeReceiverAutoCreateIT
• All added IoTDBLegacyPipeReceiverSecurityIT methods
• IoTDBPipeReceiverSessionIT
• IoTDBPipeTwoStageAggregateIT#testCountPointProcessorUsesSourceCredentials
• Spotless, Checkstyle, and git diff --check

---

This PR has:

• been self-reviewed.
• added integration tests.
• been tested in test IoTDB clusters.

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Key changed/added classes

• IoTDBLegacyPipeReceiverSecurityIT
• IoTDBLegacyPipeReceiverAutoCreateIT
• IoTDBPipeReceiverSessionIT
• IoTDBPipeTwoStageAggregateIT

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 43.49%. Comparing base (f6a844d) to head (9eab84f).

Additional details and impacted files

@@            Coverage Diff            @@
##             master   #18395   +/-   ##
=========================================
  Coverage     43.49%   43.49%           
  Complexity      374      374           
=========================================
  Files          5394     5394           
  Lines        385391   385391           
  Branches      50148    50148           
=========================================
+ Hits         167624   167626    +2     
+ Misses       217767   217765    -2     

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