[Test] Add constructor benchmarks

[mrz1836]

What Changed

• add benchmarks for constructors and utility
• update benchmark table in README with results

Why It Was Necessary

• measure performance of map constructors and Bytes2Uint16Buckets

Testing Performed

• go fmt ./...
• goimports -w .
• golangci-lint run
• go vet ./...
• go test ./...
• make run-fuzz-tests
• make govulncheck (fails: detected standard library vulnerability)
• go test -bench=. -benchmem

Impact / Risk

• no breaking changes
• adds benchmark functions only

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https://chatgpt.com/codex/tasks/task_e_68649904ab008321b9e9baf2e5b14f54

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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[Copilot]

Pull Request Overview

Introduces benchmarks for a byte‐to‐bucket utility and various map constructors, and updates the README’s benchmark table with the new results.

• Adds BenchmarkBytes2Uint16Buckets for the bucket conversion utility.
• Adds constructor benchmarks for SplitSwiss* and Swiss* map types.
• Updates the README table to include the new benchmark results.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
tx_map_benchmarks_test.go	Added benchmarks for Bytes2Uint16Buckets and multiple map constructors
README.md	Updated the benchmark table with new entries and results

Comments suppressed due to low confidence (2)

tx_map_benchmarks_test.go:10

• While you’ve added a benchmark for Bytes2Uint16Buckets, consider adding a unit test to verify its functional correctness and guard against future regressions.

// BenchmarkBytes2Uint16Buckets measures the performance of Bytes2Uint16Buckets.

tx_map_benchmarks_test.go:18

• The call to Bytes2Uint16Buckets passes a chainhash.Hash array instead of a byte slice; use hash[:] to convert the array to a slice (e.g., Bytes2Uint16Buckets(hash[:], 1024)).

		_ = Bytes2Uint16Buckets(hash, 1024)