chore: tidy to_unicode() in compat.py

[vparfait]

As part of APMAPI-1159 this is to replace code that supports < python 3.8.
Removing comments about the six library as those are outdated. six is a library to assist with python 2/3 compatibility.
Kept duck typing for future proofing and to support bytearray.

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/internal/compat.py                                              @DataDog/python-guild @DataDog/apm-core-python

[github-actions]

Bootstrap import analysis

Comparison of import times between this PR and base.

Summary

The average import time from this PR is: 272 ± 2 ms.

The average import time from base is: 274 ± 2 ms.

The import time difference between this PR and base is: -2.69 ± 0.07 ms.

Import time breakdown

The following import paths have shrunk:

ddtrace.auto 2.054 ms (0.76%)

ddtrace.bootstrap.sitecustomize 1.353 ms (0.50%)

ddtrace.bootstrap.preload 1.353 ms (0.50%)

ddtrace.internal.remoteconfig.client 0.663 ms (0.24%)

ddtrace 0.701 ms (0.26%)

ddtrace.internal._unpatched 0.058 ms (0.02%)

json 0.033 ms (0.01%)

json.decoder 0.033 ms (0.01%)

re 0.033 ms (0.01%)

enum 0.033 ms (0.01%)

types 0.033 ms (0.01%)

subprocess 0.026 ms (0.01%)

contextlib 0.026 ms (0.01%)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-06-24 07:50:22

Comparing candidate commit c22de04 in PR branch vparfait/update_unicode_compat with baseline commit 7f7f968 in branch main.

Found 0 performance improvements and 3 performance regressions! Performance is the same for 558 metrics, 3 unstable metrics.

scenario:iastaspects-format_map_aspect

• 🟥 execution_time [+432.722ns; +484.959ns] or [+13.499%; +15.129%]

scenario:iastaspects-upper_aspect

• 🟥 execution_time [+191.133ns; +236.113ns] or [+8.521%; +10.527%]

scenario:iastaspectsospath-ospathjoin_aspect

• 🟥 execution_time [+822.481ns; +966.269ns] or [+13.401%; +15.744%]