[fix](maxcompute)fix maxcompute push down predicates null pointer.

[hubgeter]

What problem does this PR solve?

Problem Summary:
This PR is a continuation of PR #55635. Based on the current investigation, the conclusion in PR #55635 appears to be incorrect — the reason why the predicate column cannot be found in the columnMap remains unclear.
To help with further debugging, this PR adds additional log information.

In addition, during the refresh table process, the MaxComputeExternalTable object remains unchanged, so the objects it holds also stay the same. When initializing the table schema, the map maintained by this object may have repeated put operations. So, move this map to MaxComputeSchemaCacheValue, which better matches its lifecycle and avoids repeated updates during table refresh.

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

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Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
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4. Which code was refactored and why was this part of the code refactored?
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[hubgeter]

run buildall

[doris-robot]

ClickBench: Total hot run time: 27.85 s

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/clickbench-tools
ClickBench test result on commit 581a4077c9c0ee7096afa09b00112ff211692015, data reload: false

query1	0.05	0.05	0.05
query2	0.09	0.06	0.06
query3	0.26	0.09	0.09
query4	1.62	0.12	0.12
query5	0.28	0.26	0.26
query6	1.19	0.66	0.64
query7	0.03	0.03	0.03
query8	0.06	0.04	0.04
query9	0.65	0.53	0.53
query10	0.59	0.59	0.57
query11	0.20	0.12	0.12
query12	0.15	0.12	0.12
query13	0.63	0.61	0.61
query14	1.02	1.01	1.01
query15	0.84	0.85	0.86
query16	0.40	0.40	0.40
query17	1.04	1.07	1.00
query18	0.22	0.20	0.21
query19	1.94	1.90	1.84
query20	0.02	0.02	0.01
query21	15.43	0.20	0.13
query22	4.96	0.06	0.05
query23	15.69	0.27	0.11
query24	2.93	1.02	0.42
query25	0.07	0.07	0.06
query26	0.14	0.14	0.13
query27	0.06	0.05	0.06
query28	4.52	1.13	0.93
query29	12.55	3.97	3.37
query30	0.29	0.14	0.12
query31	2.81	0.59	0.39
query32	3.24	0.54	0.47
query33	3.14	3.08	3.12
query34	15.79	5.16	4.59
query35	4.60	4.59	4.53
query36	0.69	0.51	0.50
query37	0.10	0.06	0.07
query38	0.07	0.05	0.04
query39	0.04	0.04	0.03
query40	0.18	0.15	0.14
query41	0.08	0.04	0.03
query42	0.04	0.04	0.04
query43	0.05	0.04	0.03
Total cold run time: 98.75 s
Total hot run time: 27.85 s

[hello-stephen]

FE Regression Coverage Report

Increment line coverage 0.00% (0/14) 🎉
Increment coverage report
Complete coverage report

[github-actions]

PR approved by at least one committer and no changes requested.

[github-actions]

PR approved by anyone and no changes requested.