chore(base-query): clean up AbstractHeapBasedIndex

[deer]

• Moves reflection out of the hot path: resolveFunction() now runs once at memoization time (via Memoizer) instead of re-resolving Field → Function inside every index(), unindex(), and reindexDynamic() call.
• Splits the single dynamicIndexableFunctionFieldsByClass memoizer into dynamicNonUniqueFunctionsByClass and dynamicUniqueFunctionsByClass, consistent with how the static function memoizers are structured.
• Extracts indexNonUnique, indexUnique, unindexNonUnique, unindexUnique, reindexNonUnique, and reindexUnique from the deeply-nested lambda bodies that previously lived inline in index(), unindex(), and reindexDynamic().
• Adds pair-level primitives putNonUnique, removeNonUnique, putUnique, removeUnique and structural helpers onNonUniquePair, onUniquePair, onExistingNonUniquePair, onExistingUniquePair to encapsulate the ConcurrentHashMap outer/inner compute patterns.
• Introduces AbstractTerminal to deduplicate the where/scope/scope() boilerplate that was verbatim across IsEqualTo, IsNotEqualTo, and Matches.
• Moves matchingUniquePairs() and matchingIndexPairs() onto Where, removing the same 6-line stream chain repeated in each terminal's findAll().
• Extracts isIndexableFunctionField, toIndexableValue, and isIndexParticipant utilities.