chore!: drop deprecated configuration, integration options & Nexus V2 Search support

[chadlwilson]

Description of Change

Drops all of the deprecated config properties, code signatures and integration options from v12 all the way back.

Happy to debate whether to retain any of these; just removed everything marked as deprecated for now.

Related issues

N/A

Have test cases been added to cover the new functionality?

yes

[Copilot]

Pull request overview

This PR removes deprecated configuration keys, deprecated integration/CLI/Ant/Maven option aliases, and drops Nexus Repository v2 search support, simplifying the public surface area and keeping only the currently supported paths.

Changes:

• Removed deprecated settings keys and legacy downloader configuration options from defaults/test fixtures.
• Dropped Nexus v2 search implementation and related tests/logging, and simplified Nexus analyzer to always use Nexus v3.
• Removed deprecated/aliased CLI + Ant + Maven plugin parameters and updated documentation accordingly.

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
utils/src/test/resources/dependencycheck.properties	Removes deprecated downloader properties from test config.
utils/src/main/java/org/owasp/dependencycheck/utils/Settings.java	Removes deprecated settings keys/constants.
utils/src/main/java/org/owasp/dependencycheck/utils/Downloader.java	Removes deprecated overload/throws surface for fetch helpers.
src/site/markdown/data/proxy.md	Removes documentation for deprecated downloader timestamp behavior.
maven/src/site/markdown/configuration.md	Removes deprecated Maven plugin property documentation.
maven/src/main/java/org/owasp/dependencycheck/maven/BaseDependencyCheckMojo.java	Removes deprecated Maven parameter and updates failure logic/message + deprecated-param handling.
core/src/test/resources/logback-test.xml	Removes test logger entry for removed Nexus v2 test.
core/src/test/resources/dependencycheck.properties	Removes deprecated downloader properties from test config.
core/src/test/java/org/owasp/dependencycheck/data/nexus/NexusV2SearchTest.java	Deletes Nexus v2 search test.
core/src/main/resources/dependencycheck.properties	Removes deprecated downloader properties from default config.
core/src/main/java/org/owasp/dependencycheck/reporting/ReportGenerator.java	Removes deprecated constructors and adjusts imports.
core/src/main/java/org/owasp/dependencycheck/Engine.java	Removes deprecated report-writing overloads and minor cleanup.
core/src/main/java/org/owasp/dependencycheck/data/nexus/NexusV3Search.java	Small refactor/cleanup (logger placement, removes unused field).
core/src/main/java/org/owasp/dependencycheck/data/nexus/NexusV2Search.java	Deletes Nexus v2 search implementation.
core/src/main/java/org/owasp/dependencycheck/analyzer/NexusAnalyzer.java	Removes Nexus v2 selection logic; always uses Nexus v3 search.
core/src/main/java/org/owasp/dependencycheck/agent/DependencyCheckScanAgent.java	Removes deprecated proxy URL accessors and reorders imports.
cli/src/site/markdown/arguments.md	Removes documentation references to deprecated CLI aliases.
cli/src/main/java/org/owasp/dependencycheck/CliParser.java	Removes deprecated CLI option constants and deprecated-option parsing.
cli/src/main/java/org/owasp/dependencycheck/App.java	Removes deprecated CLI alias support when populating settings.
ant/src/site/markdown/configuration.md	Removes documentation references to deprecated Ant property aliases.
ant/src/main/java/org/owasp/dependencycheck/taskdefs/Check.java	Removes deprecated Ant setter aliases for retired options.

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