fix: OPDS browser OOM (#403)

## Summary

- Rewrite OpdsParser to stream parsing instead of full content
- Fix OOM due to big http xml response

Closes #385 

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lib/OpdsParser/OpdsStream.cpp

@@ -0,0 +1,15 @@
+#include "OpdsStream.h"
+
+OpdsParserStream::OpdsParserStream(OpdsParser& parser) : parser(parser) {}
+
+int OpdsParserStream::available() { return 0; }
+
+int OpdsParserStream::peek() { abort(); }
+
+int OpdsParserStream::read() { abort(); }
+
+size_t OpdsParserStream::write(uint8_t c) { return parser.write(c); }
+
+size_t OpdsParserStream::write(const uint8_t* buffer, size_t size) { return parser.write(buffer, size); }
+
+OpdsParserStream::~OpdsParserStream() { parser.flush(); }