Fix CGI form/cookie data handling and CGI URL encode/decode

- CGIFormData: fix broken setSize()+read() double-length bug that
  corrupted every parsed body with a leading run of garbage bytes
  (setSize(contentLength) pre-set length before read()/write()
  appended on top of it); switch content-type checks from exact
  equality to startsWith() since a real multipart Content-Type
  always carries a boundary= parameter; implement the previously
  empty multipart/form-data branch (ordinary fields only, file
  uploads deferred to a separate upload mechanism per TODO.txt);
  restore operator[] real lookup logic (was hardcoded to echo the
  key back); default-initialize formdata to NULL; fix mismatched
  include guard (leftover from an IMFFormData.h copy-paste); drop
  the unused IMFHeader.h include that pulled in a broken,
  unrelated StreamReader.h dependency.
- CGIFormattedData: parameterize the split delimiter (was hardcoded
  to &, which silently broke cookie parsing since HTTP_COOKIE uses
  ; not &) and trim whitespace on each split token.
- MString::toCGI()/fromCGI(): were unimplemented stubs (always
  returned an empty string); implemented proper CGI percent-encode
  / percent-decode + space plus-encoding, and fixed the one caller
  that discarded fromCGIs return value instead of using it.

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

CGIFormattedData.cpp

@@ -4,27 +4,33 @@
 namespace coreutils {
    
    CGIFormattedData::CGIFormattedData() {}
-   
+
    CGIFormattedData::CGIFormattedData(ZString cgiData) {
-      if(cgiData != "") {	   
-	 cgiData.split("&");
+      parse(cgiData);
+   }
+
+   CGIFormattedData::CGIFormattedData(ZString cgiData, ZString delimiter) : delimiter(delimiter) {
+      parse(cgiData);
+   }
+
+   void CGIFormattedData::setDelimiter(ZString delimiter) {
+      this->delimiter = delimiter;
+   }
+
+   void CGIFormattedData::parse(ZString cgiData) {
+      if(cgiData != "") {
+	 cgiData.split(delimiter);
 	 for(int ix = 0; ix < cgiData.getList().size(); ++ix) {
-	    cgiData[ix].split("=");
-	    data[cgiData[ix][0]] = cgiData[ix][1];
-	    data[cgiData[ix][0]].fromCGI();
+	    ZString pair = cgiData[ix].trim();
+	    pair.split("=");
+	    data[pair[0]] = pair[1];
+	    data[pair[0]] = data[pair[0]].fromCGI();
 	 }
-      }      
+      }
    }
 
    ZString CGIFormattedData::operator=(ZString cgiData) {
-      if(cgiData != "") {	   
-	 cgiData.split("&");
-	 for(int ix = 0; ix < cgiData.getList().size(); ++ix) {
-	    cgiData[ix].split("=");
-	    data[cgiData[ix][0]] = cgiData[ix][1];
-	    data[cgiData[ix][0]].fromCGI();
-	 }
-      }
+      parse(cgiData);
       return cgiData;
-   }      
+   }
 }