test(tree): Add simple plain text insert/remove character op-size benchmark tests

[Josmithr]

Insert character

Scenario	Total Op Size (Bytes)	Total Ops
Insert 1 character into empty string	584	1
Insert 1 character into long string (1000 characters)	598	1

Remove character

Scenario	Total Op Size (Bytes)	Total Ops
Remove 1 character from short string (1 character)	413	1
Remove 1 character from long string (1000 characters)	427	1

[Josmithr]

Note for reviewers: this code was extracted from opSize.bench.ts for reuse.

[Copilot]

Pull request overview

Adds op-size benchmark coverage for the TextDomain plain-text editing path, and factors common op-capture/stat logic into a shared utility to reuse across benchmark suites.

Changes:

• Add new TextDomain benchmarks for inserting/removing a single character in short and long strings, reporting total/max op sizes and op count.
• Extract createConnectedTree, registerOpListener, and op-size stats helpers into a new opBenchmarkUtilities.ts.
• Refactor opSize.bench.ts to use the shared utilities and remove duplicated helper code/imports.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
packages/dds/tree/src/test/shared-tree/textDomain.bench.ts	New measurement benchmarks for single-character insert/remove in TextAsTree, reporting op-size stats.
packages/dds/tree/src/test/shared-tree/opSize.bench.ts	Removes locally-defined op-capture/stats helpers in favor of the shared benchmark utilities.
packages/dds/tree/src/test/shared-tree/opBenchmarkUtilities.ts	Introduces shared helpers for creating a connected test tree, capturing submitted ops, and computing op-size stats.