Address reviewer feedback on the Maven toolchains dedup logic:
- Treat jdk toolchains without a string `provides.id` as non-deduplicatable
and use optional access when comparing ids, so partially-formed or
nonstandard toolchains.xml files no longer crash setup.
- Preserve the existing `<toolchains>` root attributes (xmlns,
schemaLocation, …) when present, falling back to the 1.1.0 defaults only
for attributes the existing file is missing. This avoids silently
rewriting user-managed metadata or changing the effective namespace.
Adds tests covering custom root attributes and id-less jdk toolchains, and
rebuilds dist/.
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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