RFR: 8309527: Improve test proxy performance

[Daniel Jeliński]

Please review this change to introduce buffering in the tunnelling proxy implementations.

Copying network data one byte at a time is very inefficient. ProxyAuthDisabledSchemesSSL is 10 seconds faster (from 40 down to 30s) on my Windows machine with these changes.

I did not quantify the improvements in other tests affected by this change; I only verified that they continue to pass.

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Commit messages:
 - Update copyright
 - Buffer transferred data

Changes: https://git.openjdk.org/jdk/pull/14329/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14329&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309527
  Stats: 29 lines in 5 files changed: 5 ins; 0 del; 24 mod
  Patch: https://git.openjdk.org/jdk/pull/14329.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14329/head:pull/14329

PR: https://git.openjdk.org/jdk/pull/14329