ref: Make SentryTracer sub class of SentrySpan (#2675)

SentryTracer is the core of performance, and it gets bigger and bigger with each new feature, therefore is getting harder to understand it.

This is the first step to reduce it. The goal in the future is to extract more behavior from it and use DI as replacement.

Samples/iOS-SwiftUI/iOS-SwiftUI-UITests/LaunchUITests.swift

@@ -24,5 +24,4 @@ class LaunchUITests: XCTestCase {
         XCTAssertEqual(transactionName.label, "Content View Body")
         XCTAssertEqual(childParentId.label, transactionId.label)
     }
-
 }

Sources/Sentry/SentrySpan.m

@@ -7,6 +7,8 @@
 #import "SentryLog.h"
 #import "SentryMeasurementValue.h"
 #import "SentryNoOpSpan.h"
+#import "SentrySerializable.h"
+#import "SentrySpanContext.h"
 #import "SentrySpanId.h"
 #import "SentryTime.h"
 #import "SentryTraceHeader.h"
@@ -24,12 +26,10 @@ @implementation SentrySpan {
     BOOL _isFinished;
 }
 
-- (instancetype)initWithTracer:(SentryTracer *)tracer context:(SentrySpanContext *)context
+- (instancetype)initWithContext:(SentrySpanContext *)context
 {
     if (self = [super init]) {
-        SENTRY_LOG_DEBUG(
-            @"Created span %@ for trace ID %@", context.spanId.sentrySpanIdString, tracer.traceId);
-        _tracer = tracer;
+        SENTRY_LOG_DEBUG(@"Created span %@", context.spanId.sentrySpanIdString);
         self.startTimestamp = [SentryCurrentDate date];
         _data = [[NSMutableDictionary alloc] init];
         _tags = [[NSMutableDictionary alloc] init];
@@ -46,6 +46,14 @@ - (instancetype)initWithTracer:(SentryTracer *)tracer context:(SentrySpanContext
     return self;
 }
 
+- (instancetype)initWithTracer:(SentryTracer *)tracer context:(SentrySpanContext *)context
+{
+    if (self = [self initWithContext:context]) {
+        _tracer = tracer;
+    }
+    return self;
+}
+
 - (id<SentrySpan>)startChildWithOperation:(NSString *)operation
 {
     return [self startChildWithOperation:operation description:nil];