[Iotdb-2041] Added javadocs for Session and SessionPool and made methods consistent

[A0R0P0I7T]

What is changed

This PR adds and improves Javadoc for Session and SessionPool.

• Added missing Javadoc for constructors, public methods, and selected helper methods
• Improved clarity of some existing Javadoc where needed
• Kept the documentation simple and consistent across both classes

Consistency updates

• Ensured similar methods in Session and SessionPool have consistent descriptions

• Added references between related methods using @see

• Clarified the relation between:

  • Session.insertRecordsOfOneDevice
  • SessionPool.insertOneDeviceRecords

Fixes Issue:

• https://issues.apache.org/jira/browse/IOTDB-2041?filter=-4&jql=project%20%3D%20IOTDB%20AND%20text%20~%20%22javadoc%22%20order%20by%20created%20DESC

Notes

• Did not modify any method logic or signatures
• Avoided changing existing Javadoc unless necessary
• Focused only on missing or unclear documentation

Why this change is needed

Improves readability and usability of the client API by making method behavior easier to understand and documentation more consistent.

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This PR has:

• been self-reviewed.
  • concurrent read
  • concurrent write
  • concurrent read and write
• added Javadocs for most classes and all non-trivial methods.

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