fix(composer): map DDTrace\\OpenFeature\\ namespace to src/DDTrace/OpenFeature/

Composer PSR-4 autoload only mapped DDTrace\\ to src/api/, so tests and
host code that reference DDTrace\\OpenFeature\\BridgeResultMapper etc
failed to autoload. Add explicit DDTrace\\OpenFeature\\ mapping before
the catch-all DDTrace\\ entry so PSR-4 resolution hits it first.

Verified: vendor/bin/phpunit tests/OpenFeature passes 143/143.

Author: leoromanovsky

composer.json

@@ -46,6 +46,7 @@
     },
     "autoload": {
         "psr-4": {
+            "DDTrace\\OpenFeature\\": "./src/DDTrace/OpenFeature/",
             "DDTrace\\": "./src/api/"
         }
     },