[lake] Optimize TableLookup finder creation

[KiteSoar]

Purpose

Linked issue: close #2521

Brief change log

• Enhance TableLookup.createLookuper() to intelligently route lookup requests:
  • Create PrimaryKeyLookuper when lookup columns match primary key
  • Create PrefixKeyLookuper when lookup columns are valid prefix key
  • Fail-fast with clear error message for invalid lookup columns

Tests

• Add TableLookupTest with 10 test cases covering:
  • Primary key lookup (with/without lookupBy, partitioned/non-partitioned)
  • Prefix key lookup (single/multiple columns, partitioned/non-partitioned)
  • Invalid inputs (out-of-order, empty, non-primary/non-prefix columns)
  • Log table rejection

API and Format

None

Documentation

None

[KiteSoar]

Hi @luoyuxia Could you please help review when you got some time?

[Copilot]

Pull request overview

Optimizes TableLookup.createLookuper() to choose between primary-key and prefix-key lookup based on provided lookup columns, and adds tests to validate the routing and failure behavior (linked to #2521).

Changes:

• Update TableLookup.createLookuper() to route to PrimaryKeyLookuper for full-PK lookups and PrefixKeyLookuper for prefix-key lookups, otherwise throw an error.
• Add TableLookupTest covering primary-key routing, prefix-key routing, and invalid input cases.
• Adjust FlussLakeTableITCase to consistently use lookupBy(...) when creating lookupers.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
fluss-client/src/main/java/org/apache/fluss/client/lookup/TableLookup.java	Adds routing logic and validation/error path for lookuper creation based on lookup columns.
fluss-client/src/test/java/org/apache/fluss/client/lookup/TableLookupTest.java	New unit tests validating routing and invalid-argument behavior.
fluss-client/src/test/java/org/apache/fluss/client/table/FlussLakeTableITCase.java	Updates integration test to always specify lookup columns via lookupBy(...).

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