feat: add support for Java-Agent layer

[Sashwatdas123]

Details :

• Adds --java-agent true option to layers install; attaches NewRelicAgentJava layer, sets AWS_LAMBDA_EXEC_WRAPPER=/opt/newrelic-java-handler and keeps the
  original handler unchanged
• --slim auto-selects NewRelicAgentJava-slim without prompting
  • -u supports switching between OpenTracing and Java Agent families with full Environment variable and
    handler
• AWS_LAMBDA_EXEC_WRAPPER handling scoped to Java runtimes only; uninstall
  auto-detects the active family and cleans up accordingly
• Existing OpenTracing behaviour unchanged when --java-agent is omitted

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.52%. Comparing base (59b796b) to head (74782e0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #382      +/-   ##
==========================================
+ Coverage   70.04%   70.52%   +0.48%     
==========================================
  Files          20       20              
  Lines        1876     1893      +17     
==========================================
+ Hits         1314     1335      +21     
+ Misses        562      558       -4     

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