Deprecate JournalOptions.Adapters property in favor of callback API

[Aaronontheweb]

Fixes #665

Summary

The Adapters property on JournalOptions created confusion by providing two competing patterns for configuring event adapters. This PR deprecates the property in favor of the unified callback pattern introduced in PR #662.

Problem

Having two ways to configure event adapters was:

• ❌ Confusing - No clear guidance on which pattern to use
• ❌ Inconsistent - Health checks only support callbacks
• ❌ Undocumented - Users could use both simultaneously with unclear merge semantics
• ❌ Dangerous - Property initialized with dummy builder that could cause NRE

Solution

1. Mark property as [Obsolete] with clear migration guidance pointing to issue Deprecate JournalOptions.Adapters property in favor of unified callback API #665
2. Remove internal usage - Stop reading the property in JournalOptions.Build()
3. Add regression test - Verify deprecated property is ignored and callbacks work

Changes

• JournalOptions.cs:78 - Added [Obsolete] attribute to Adapters property
• JournalOptions.cs:105 - Removed Adapters.AppendAdapters(sb) call
• EventAdapterSpecs.cs:134-207 - Added DeprecatedAdaptersPropertySpec regression test

Benefits

✅ Single, consistent pattern for configuring adapters and health checks
✅ Cleaner API surface - options contain only configuration data
✅ Clear migration path with deprecation warning
✅ No silent failures - deprecated property is truly ignored

Migration Example

Before (deprecated):

var journalOptions = new SqlJournalOptions(true)
{
    Adapters = new AkkaPersistenceJournalBuilder("sql", builder)
};
journalOptions.Adapters.AddWriteEventAdapter<Foo>("foo", [typeof(Bar)]);

builder.WithJournal(journalOptions);

After (recommended):

var journalOptions = new SqlJournalOptions(true);

builder.WithJournal(
    journalOptions,
    journal => journal.AddWriteEventAdapter<Foo>("foo", [typeof(Bar)]));

Testing

All 17 persistence hosting tests pass, including new regression test that verifies:

• Deprecated property is ignored (doesn't configure adapters)
• Callback pattern works correctly
• Uses #pragma warning disable to test deprecated API without warnings

Note

This is Phase 1 of the deprecation plan. The property will be removed entirely in v1.6.0.