fix: upgrade PMD to 7.26.0 to and correct issues

[szysas]

Summary

• Upgrades PMD to 7.27.0 to address CVE-2025-23215 / Dependabot alert #4.
• Declares explicit pmd dependencies in build.gradle.kts so Dependabot automatically tracks future PMD updates, isolated into separate PRs via .github/dependabot.yml.
• Updates pmd-rules.xml for PMD 7 compatibility and disables PMD on the deprecated lwm2m module.
• Fixes all codebase violations raised by PMD 7 rules and adds unit tests to maintain 100% diff coverage.

PMD Rules Fixed in Code

• LooseCoupling: Switched from concrete types (ArrayList, LinkedList, ConcurrentHashMap) to interfaces (List, ConcurrentMap, Map).
• EnumComparison: Replaced .equals() with == on enum comparisons.
• ModifierOrder: Standardized Java modifier order (e.g. public static final).
• UnusedReturnValue: Replaced unchecked InputStream.read() with Files.readAllBytes().
• UnnecessaryFullyQualifiedName: Removed redundant class qualifiers already in scope.
• ImplicitFunctionalInterface: Added @FunctionalInterface annotations to SAM interfaces.
• UnnecessaryBoxing: Removed explicit longValue() conversions where automatic unboxing/overloads apply.
• InsufficientStringBufferDeclaration & ConsecutiveAppendsShouldReuse: Sized StringBuilder capacity appropriately and chained .append() calls.
• UseDiamondOperator & UselessParentheses: Cleaned up diamond syntax and redundant parentheses.

Rules Excluded in pmd-rules.xml

• Excluded subjective/disruptive rules that alter functional branching (SimplifyBooleanReturns, SimplifyConditional, LiteralsFirstInComparisons, AvoidDeeplyNestedIfStmts, ExceptionAsFlowControl, AvoidSynchronizedStatement).
• Updated rule exclusions to PMD 7 naming (InstantiableUtilityClass, TypeParameterNamingConventions, PublicMemberInNonPublicType, BooleanGetMethodName).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.92%. Comparing base (01f2fa4) to head (ef16df8).

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #150      +/-   ##
============================================
+ Coverage     92.86%   92.92%   +0.06%     
- Complexity     2141     2142       +1     
============================================
  Files           135      135              
  Lines          4762     4761       -1     
  Branches        637      637              
============================================
+ Hits           4422     4424       +2     
+ Misses          194      192       -2     
+ Partials        146      145       -1     

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