perf: Reuse a single JsonProvider.

This speeds up the formatter significantly.

Before:

    Benchmark                                         Mode  Cnt     Score      Error  Units
    FormatterBenchmark.massivelyStructuredLogRecord  thrpt   10  6552.727 ± 2169.572  ops/s
    FormatterBenchmark.simpleLogRecord               thrpt   10  8126.699 ± 2259.912  ops/s
    FormatterBenchmark.structuredLogRecord           thrpt   10  5594.849 ± 1129.151  ops/s

After:

    Benchmark                                         Mode  Cnt       Score        Error  Units
    FormatterBenchmark.massivelyStructuredLogRecord  thrpt   10  137879.001 ±  30467.644  ops/s
    FormatterBenchmark.simpleLogRecord               thrpt   10  896085.217 ± 249890.421  ops/s
    FormatterBenchmark.structuredLogRecord           thrpt   10  553428.807 ± 194787.754  ops/s

Change-Id: If184327a4ff0de0d92b769493dbf6270ba3a8c8e
diff --git a/core/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Formatter.java b/core/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Formatter.java
index c4e36de..72b0b50 100644
--- a/core/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Formatter.java
+++ b/core/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Formatter.java
@@ -4,6 +4,7 @@
 
 package eu.mulk.quarkus.googlecloud.jsonlogging;
 
+import jakarta.json.spi.JsonProvider;
 import java.io.PrintWriter;
 import java.io.StringWriter;
 import java.util.ArrayList;
@@ -38,6 +39,7 @@
 
   private final List<StructuredParameterProvider> parameterProviders;
   private final List<LabelProvider> labelProviders;
+  private final JsonProvider json;
 
   /**
    * Constructs a {@link Formatter} with custom configuration.
@@ -53,6 +55,7 @@
       Collection<LabelProvider> labelProviders) {
     this.parameterProviders = List.copyOf(parameterProviders);
     this.labelProviders = List.copyOf(labelProviders);
+    this.json = JsonProvider.provider();
   }
 
   /**
@@ -152,7 +155,7 @@
             ndc,
             logRecord.getLevel().intValue() >= 1000 ? ERROR_EVENT_TYPE : null);
 
-    return entry.json().build().toString() + "\n";
+    return entry.json(json).build().toString() + "\n";
   }
 
   /**