Improve SharedTree comparator functions

[noencke]

• Removes rebaser usages of the sorted-btree library's defaultComparator, which is slow (and came up in performance profiling).
• Updates TupleBTrees to require comparators for their elements, and adds some additional compile time safety around the typing.
• Fixes a bug in the RevisionTag comparator which compared "root" equal to every number.
• Adds and removes core comparators in our utils folder and updated them with consistent naming
• Adds unit tests for the comparators

[Copilot]

Pull request overview

This PR improves comparator functions in the tree package by fixing a critical bug and enhancing performance:

Changes:

• Fixes a bug in comparePartialRevisions (formerly compareRevisions) that incorrectly compared "root" string equal to all numbers
• Adds new comparator utility functions (compareNumbers, comparePartialNumbers, comparePartialStrings) with proper handling of edge cases (NaN, Infinity, undefined)
• Removes defaultComparator usage from sorted-btree library (performance improvement)
• Introduces newChangeAtomIdBTree helper to replace manual newTupleBTree calls with proper comparators
• Updates newTupleBTree and mergeTupleBTrees signatures for better API design
• Adds comprehensive unit tests for all comparators

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/dds/tree/src/util/utils.ts	Removes Named interface and compareNamed function; adds new comparator functions (compareNumbers, comparePartialNumbers, comparePartialStrings) with proper edge case handling
packages/dds/tree/src/util/index.ts	Updates exports to include new comparator functions and remove deleted ones
packages/dds/tree/src/util/bTreeUtils.ts	Updates newTupleBTree to accept comparator parameter and mergeTupleBTrees to require non-undefined first parameter; improves tuple comparison implementation
packages/dds/tree/src/test/util/utils.spec.ts	Adds comprehensive unit tests for all new comparator functions including edge cases
packages/dds/tree/src/test/shared-tree/sharedTreeChangeCodec.spec.ts	Updates to use newChangeAtomIdBTree instead of newTupleBTree
packages/dds/tree/src/test/feature-libraries/modular-schema/modularChangesetUtil.ts	Updates to use newChangeAtomIdBTree instead of newTupleBTree
packages/dds/tree/src/test/feature-libraries/modular-schema/modularChangeFamily.spec.ts	Updates all usages to use newChangeAtomIdBTree with proper typed comparators
packages/dds/tree/src/feature-libraries/modular-schema/modularChangeFamily.ts	Implements newFieldIdKeyBTree with proper comparators; updates all BTree creation to use typed functions
packages/dds/tree/src/feature-libraries/modular-schema/modularChangeCodecV1.ts	Updates to use newChangeAtomIdBTree for decoding
packages/dds/tree/src/feature-libraries/modular-schema/index.ts	Changes from export type to export to also export newCrossFieldKeyTable function
packages/dds/tree/src/feature-libraries/index.ts	Adds export for newChangeAtomIdBTree
packages/dds/tree/src/feature-libraries/changeAtomIdBTree.ts	Adds newChangeAtomIdBTree helper function with proper comparators for ChangeAtomId tuples
packages/dds/tree/src/core/rebase/types.ts	Renames compareRevisions to comparePartialRevisions and fixes bug where string "root" compared equal to all numbers
packages/dds/tree/src/core/rebase/index.ts	Updates export name to comparePartialRevisions
packages/dds/tree/src/core/index.ts	Exports comparePartialRevisions as compareRevisions for backward compatibility
.gitignore	Adds .worktrees/ entry (appears unrelated to PR purpose)