fix: resolve ~400 SonarQube maintainability and Roslyn analyzer issues

[rygel]

Summary

Fixes ~400 SonarQube maintainability issues across 68 files, including:

High-impact fixes:

• MA0076 (136): Add CultureInfo.InvariantCulture to interpolated strings to avoid culture-sensitive ToString() calls
• CA1860 (16): Replace .Any() with .Count > 0 for collections with Count property
• CA1859 (15): Use concrete return types instead of interface return types
• CA1861 (14): Extract inline arrays to static readonly fields
• CA1869 (11): Cache JsonSerializerOptions as static readonly fields
• MA0159 (12): Use Order() instead of OrderBy()
• MA0089 (18): Use char overloads instead of single-char strings
• MA0020 (13): Replace .All() with .TrueForAll() for List<T>

Reliability fixes:

• S6677 (1): Make log template placeholders unique
• S108 (4): Fill empty catch blocks in notification services
• S1118 (1): Make ProviderRefreshConfigSelector a static class
• S4487 (1): Remove unread private field _configSelector
• S2139 (1): Pass exception to logger with context

Code quality:

• xUnit1030 (23): Remove ConfigureAwait(false) from test methods
• CA1816 (5): Add GC.SuppressFinalize to Dispose methods
• MA0042 (5): Use await using for IAsyncDisposable
• MA0053 (5): Seal internal/private classes
• SYSLIB1054 (1): Use LibraryImport instead of DllImport
• CA1822 (3): Make non-instance methods static
• CA1835 (2): Use Memory<byte> overloads
• CA1845 (1): Use AsSpan + string.Concat
• SA1210, SA1502: Style/Formatting fixes

Note: 54 VSTHRD111 (ConfigureAwait) issues in test code are intentionally skipped - they conflict with xUnit1030.

Test plan

• dotnet build - 0 errors, 0 warnings
• All 1,491 tests pass across 3 test projects
• SonarQube scan to verify issue reduction