Fix spelling errors

Most errors found with:

codespell -L cach,thst,odly,aslo,parm,parms,inpu,ges,prset,pevent,ptd,pring,valu,noo,noe,ned,inout,ro,siz,froms,nd,fo,singl,sart,multy,tthe,allong,ment,inate,nodel,tring,alse,ture,thi,wille,numer

Some more manually found (its -> it's)

c++20: Do not use apostrophe (e.g. can't) in unquoted #error message

modules/ca/src/client/netiiu.cpp

@@ -167,7 +167,7 @@ void netiiu::uninstallChanDueToSuccessfulSearchResponse (
     epicsGuard < epicsMutex > &, nciu &, const epicsTime & )
 {
     throw std::runtime_error (
-        "search response occured when not attached to udpiiu?" );
+        "search response occurred when not attached to udpiiu?" );
 }
 
 bool netiiu::searchMsg (