currency: Fix edge case in NewCode where all string characters are digits (#1593)

* add fixes and test

* glorious: nits, privatise upper case field, add item field for case sensitivity for format checks, rm dead code.

* fix potential panic

* gk/glorious: nits

* gk: nits and other things

* improve commentary lol

* glorious+gk: nits and improvements (with no sillyness this time)

* Update currency/pairs.go

Co-authored-by: Adrian Gallagher <adrian.gallagher@thrasher.io>

* thrasher: nitssssss

* linter: fix

* bye bye silly boy

---------

Co-authored-by: Ryan O'Hara-Reid <ryan.oharareid@thrasher.io>
Co-authored-by: Adrian Gallagher <adrian.gallagher@thrasher.io>

gctscript/wrappers/gct/gctwrapper_test.go

@@ -96,10 +96,10 @@ var (
 		Value: "error",
 	}
 	currencyPair = &objects.String{
-		Value: "BTCUSD",
+		Value: "BTC-USD",
 	}
 	delimiter = &objects.String{
-		Value: "",
+		Value: "-",
 	}
 	assetType = &objects.String{
 		Value: "spot",