Add StreamReader and rebuild Parser/LineParser/IMFHeader/IMFBoundary on it

Introduces StreamReader to accumulate socket data delivered in arbitrary
chunks into one buffer, so a Parser can build an object (a line, a header
block, a MIME boundary) that spans any number of packets without losing
its place. Parser is redesigned around this: no longer inherits MString
(was redundant with its own buffer member), takes a StreamReader&, and
drives a resumable COMPLETE/INCOMPLETE/DATA_AVAIL state-machine protocol
via doParse(). LineParser, IMFHeader, and IMFBoundary are rewritten as
real, working resumable parsers against the shared buffer instead of the
previous non-compiling stubs (mismatched constructors/return types, a
syntax error, checkParse() never implemented).

IMFFormData is left as the stub it already was, just restored to
compiling against the new IMFHeader signature - fully wiring it up needs
IMFMultipart/IMFText migrated to StreamReader too, out of scope here.

Verified with real runtime tests (not just compilation) covering data
split mid-line, mid-CRLF, mid-header-fold, and mid-boundary-marker across
separate feed() calls, plus StreamReader::compact(). Along the way fixed
a header-value bug (space after ':' wasn't skipped) and a double
cursor-offset subtraction bug in two places caused by forgetting that
ZString::getLength() is already cursor-relative, not the raw buffer size.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

LineParser.cpp

@@ -1,18 +1,26 @@
 #include "LineParser.h"
-#include "Exception.h"
-#include <unistd.h>
 
 namespace coreutils {
 
-   LineParser::LineParser(StreamReader &reader) {
-      
-   }
-      
-   int LineParser::parse() {
-      
+   LineParser::LineParser(StreamReader &reader) : Parser(reader) {}
 
-
-      
+   Parser::Status LineParser::parse() {
+      MString &buffer = reader.getBuffer();
+      char *lineStart = buffer.getCursor();
+      ZString term("\n");
+      int pos = buffer.find(term);
+      if (pos < 0)
+         return Status::INCOMPLETE;
+      char *lineEnd = buffer.getCursor();
+      if (lineEnd > lineStart && *(lineEnd - 1) == '\r')
+         --lineEnd;
+      line = ZString(lineStart, lineEnd - lineStart);
+      buffer.setCursor(buffer.getCursor() + 1);
+      return Status::COMPLETE;
    }
-            
-}
+
+   ZString LineParser::getLine() {
+      return line;
+   }
+
+}