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.h

@@ -1,18 +1,40 @@
 #ifndef __LineParser_h__
 # define __LineParser_h__
 
-#include "StreamReader.h"
 #include "Parser.h"
 
 namespace coreutils {
-   
+
+   ///
+   /// LineParser builds one line of text at a time from the shared
+   /// StreamReader - terminated by LF or CRLF, either accepted, the
+   /// terminator itself is not included in getLine(). Resumable: if no
+   /// terminator has arrived yet, parse() reports INCOMPLETE and leaves the
+   /// cursor exactly where it started, so the same unconsumed bytes are
+   /// re-scanned (along with whatever new data arrived) on the next call.
+   ///
+
    class LineParser : public Parser {
-      
+
     public:
+
       LineParser(StreamReader &reader);
 
-      int parse() override;
-      
+      ///
+      /// Valid once doParse() has returned Status::COMPLETE - the line that
+      /// was parsed, with its terminator stripped.
+      ///
+
+      ZString getLine();
+
+    protected:
+
+      Status parse() override;
+
+    private:
+
+      ZString line;
+
    };
 
 }