Implement proper YAML path navigation and complex type support

- YAML resolver now supports full path navigation (e.g., production.primary.host)
- Both JSON and YAML resolvers return YAML-formatted data for complex types
- This allows proper type preservation when loading objects/arrays from files
- Updated convertToType to parse YAML returned by resolvers
- Added comprehensive tests for YAML path navigation including arrays
- Fixed JSON resolver to support "." path for entire document
- All README examples now work correctly

The key insight was that resolvers should return YAML strings for complex
types, which can then be parsed and merged into the configuration structure,
preserving the original types (maps, arrays) instead of flattening to strings.

test/config.yaml

@@ -14,8 +14,8 @@ api:
   tls_host: ${JSON:./test/hosts.json:tls_sni_host.0}
 
 database:
-  host: ${YAML:./test/data.yaml:'.database.host'}
-  version: ${YAML:./test/data.yaml:'.version'}
+  host: ${YAML:./test/data.yaml:database.host}
+  version: ${YAML:./test/data.yaml:version}
 
 nested:
   value: ${ENV:NESTED_${ENV:TEST_ENV_SUFFIX}}

test/database.yaml

@@ -0,0 +1,20 @@
+production:
+  primary:
+    host: prod-db-primary.example.com
+    port: 5432
+    username: prod_user
+  replica:
+    host: prod-db-replica.example.com
+    port: 5432
+
+staging:
+  primary:
+    host: staging-db.example.com
+    port: 5432
+    username: staging_user
+
+development:
+  primary:
+    host: localhost
+    port: 5432
+    username: dev_user

test/features.yaml

@@ -0,0 +1,15 @@
+features:
+  analytics:
+    enabled: true
+    provider: google
+    tracking_id: UA-123456
+  new_ui:
+    enabled: false
+    rollout_percentage: 25
+  rate_limiting:
+    enabled: true
+    requests_per_minute: 100
+
+settings:
+  debug: false
+  log_level: info