Event stream protocol tests (#2803)

* Add event stream protocol test trait

* Add event stream protocol tests for restJson1

* Use values greater than max int for long tests

* Use text blocks for JSON bodies

This updates event stream protocol tests to use text blocks for the
JSON bodies to make them easier to read.

* Use b64 encoding for event test blobs

* Add event bytes to event stream tests

* Use utf8 bytes explicitly

* Add blob support to NodeMapper

This adds blob support to NodeMapper, serializing to and from base64
encoded string nodes.

Author: JordonPhillips

.changes/next-release/feature-3c0c9d0841cb39ac6fabcbc085d11f94ce6def67.json

@@ -0,0 +1,7 @@
+{
+  "type": "feature",
+  "description": "Added protocol tests for event streaming in restJson1.",
+  "pull_requests": [
+    "[#2803](https://github.com/smithy-lang/smithy/pull/2803)"
+  ]
+}

.changes/next-release/feature-783557f3624987ca34a0269dc18e0b8aa6e4a19f.json

@@ -0,0 +1,7 @@
+{
+  "type": "feature",
+  "description": "Added support for (de)serializing byte arrays to/from base64-encoded string nodes to `NodeMapper`.",
+  "pull_requests": [
+    "[#2803](https://github.com/smithy-lang/smithy/pull/2803)"
+  ]
+}

.changes/next-release/feature-b1c486e0513a86003dcfc7a64a7308e31c52fdbe.json

@@ -0,0 +1,7 @@
+{
+  "type": "feature",
+  "description": "Added a new `eventStreamProtocolTests` trait to enable writing shared test suites for event streams just as has been done for standard HTTP protocol requests and responses.",
+  "pull_requests": [
+    "[#2803](https://github.com/smithy-lang/smithy/pull/2803)"
+  ]
+}