Migrate SolrJ client APIs for 10.0.0

[skrcode]

Completes #3953 by migrating the backend to the SolrJ 10 client API:

• add the split solr-solrj-jetty artifact and use the renamed Jetty client
  implementations
• move SolrQuery and streaming response types to their SolrJ 10 packages
• replace the removed client binder accessor with DocumentObjectBinder.INSTANCE

Verification (JDK 21):

• mvn -q -pl backend -am clean compile -DskipTests — passed
• mvn -q -pl backend test-compile -DskipTests — passed
• remote mvn -q -pl backend test — 1,121 tests executed with 0 assertion
  failures; the run could not complete because the disposable environment has
  no Docker daemon, producing two Testcontainers setup errors for HANA and
  ClickHouse
• git diff --check — passed

Development assistance: prepared in Codex with the maintainer-intent,
fast-execution, remote-Java, and diff-review skills from
JAIPilot. The exact source was executed
in a disposable remote workspace that was destroyed after the run. Execution profile:
gpt-5.6-sol · xhigh · fast.

[awildturtok]

Hi @skrcode, thank your for your contribution.

We generally avoid unsolicited code from unknown third parties. Please refrain from creating pull requests in the future, unless you've been in contact with us.

Best,
awildturtok

[skrcode]

sure, no worries. thanks anyways !