Optimize SQL rewrite token traversal

[FlyingZC]

Fixes #ISSUSE_ID.

Changes proposed in this pull request:

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• My code follows the code of conduct of this project.
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[FlyingZC]

Decision

• Merge Verdict: Mergeable
• Reviewed Scope: PR Optimize route lookup and sharding table find #38794 latest head d17cbba0b5e05ff47890060f53653ecc73ce7c43, merge-base 908ff08cea2925d387983f42580c5fc493fe3228; local diff file list matched GitHub / pulls/38794/files. Reviewed features/sharding/core/src/main/java/org/apache/shardingsphere/sharding/rule/ShardingRule.java, infra/executor/src/main/java/org/apache/shardingsphere/ infra/executor/sql/prepare/driver/DriverExecutionPrepareEngine.java, and infra/route/core/src/main/java/org/apache/shardingsphere/infra/route/context/RouteUnit.java.
• Not Reviewed Scope: GitHub Actions / CI status and full repository build.
• Need Expert Review: No.

Basis

• features/sharding/core/src/main/java/org/apache/shardingsphere/sharding/rule/ShardingRule.java:309 simplifies containsKey + get into one null-aware lookup. Existing missing-table
  and null-table-name behavior is preserved by the existing rule tests.
• infra/route/core/src/main/java/org/apache/shardingsphere/infra/route/context/RouteUnit.java:85 hoists the datasource mismatch check before scanning table mappers. This keeps the same
  datasource-first matching semantics and avoids repeated invariant checks inside the loop.
• infra/executor/src/main/java/org/apache/shardingsphere/infra/executor/sql/prepare/driver/DriverExecutionPrepareEngine.java:97 and infra/executor/src/main/java/org/apache/ shardingsphere/infra/executor/sql/prepare/driver/DriverExecutionPrepareEngine.java:109 use pre-sized ArrayList for append-only lists whose target sizes are already known. Order and
  ExecutionGroup behavior are unchanged.

Verification

• git diff --name-status $(git merge-base upstream/master upstream/pr/38794)..upstream/pr/38794 matched the GitHub file list.
• git diff --check $(git merge-base upstream/master upstream/pr/38794)..upstream/pr/38794 passed with exit code 0.
• ./mvnw -pl infra/route/core,features/sharding/core,infra/executor -am -DskipITs -Dspotless.skip=true -Dcheckstyle.skip=true -Dsurefire.failIfNoSpecifiedTests=false -Dtest=RouteUnitTest,RouteContextTest,ShardingRuleTest test passed with exit code 0.
• Surefire confirmed RouteUnitTest 6 tests, RouteContextTest 11 tests, and ShardingRuleTest 71 tests passed with 0 failures/errors/skips.