[core] Harden and slim FM index storage

[JingsongLi]

Purpose

• Freeze the FM V1 checksum contract as IEEE CRC32 over stored bytes plus the compression ID.
• Align dense-query handling with Milvus: keep selective FM locate, but decline expensive intervals so the normal data path scans source values.
• Remove duplicated verification-value pages, their configuration, feature flag, reader/writer paths, and dead byte-pattern matcher.
• Avoid repeated physical reads with zero or undersized caches, including block-wise null bitmap scans.
• Cross-check container and partition feature flags, refresh the unpublished V1 golden fixture, and update the FM documentation.

Storage impact

For uncompressed or hard-to-compress text, the index no longer carries roughly the full source string bytes plus 4 bytes per row and page metadata. The golden fixture shrinks from 1,926 to 1,860 bytes for 14 source bytes across four rows.

Tests

• mvn -pl paimon-common -DwildcardSuites=none -Dtest=FMGlobalIndexTest,FMIndexSuffixArrayTest test
• 25 tests passed; checkstyle, spotless, and enforcer passed.

[utafrali]

The PR is well-structured and the test coverage for the new paths is solid. The one blocking concern is the undocumented format break: switching from CRC32C to IEEE CRC32 without incrementing VERSION makes old and new files silently incompatible, which is fixable with a single constant change and a clear error message in the footer reader.