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>

Parser.cpp

@@ -1,19 +1,21 @@
 #include "Parser.h"
-#include "StreamReader.h"
 
 namespace coreutils {
 
-   Parser::Parser(int socket) : socket(socket) {}
+   Parser::Parser(StreamReader &reader) : reader(reader) {}
 
    Parser::~Parser() {}
 
-   Status Parser::doParse() {
+   Parser::Status Parser::doParse() {
+      Status status;
+      do {
+         status = parse();
+      } while (status == Status::DATA_AVAIL);
+      return status;
    }
 
-   bool Parser::checkParse(Parser &parser);
-
-   Status Parser::parse() {
-      return Status::COMPLETE;
+   bool Parser::checkParse(Parser &parser) {
+      return parser.doParse() == Status::COMPLETE;
    }
-      
+
 }