refactor session part and statement part to improve code readability

[googs1025]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

• refactor session part to improve readability. We can reduce if-else branches and reduce code complexity
• refactor statement part

Which issue(s) this PR fixes:

Special notes for your reviewer:

Does this PR introduce a user-facing change?

None

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

None

[googs1025]

/cc @lowang-bh @hwdef @Monokaix

[lowang-bh]

/lgtm

[volcano-sh-bot]

New changes are detected. LGTM label has been removed.

[volcano-sh-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[lowang-bh]

/hold

[Monokaix]

/hold
Any consideration here?

[lowang-bh]

Session refact is ok. The statement refact has some information lose. The log is important and should be easy to debug issue in production env.

[googs1025]

Session refact is ok. The statement refact has some information lose. The log is important and should be easy to debug issue in production env.

I have kept most of the logs.
can you help me to review it, and point it out to me if I missed anything and I will modify it immediately.