Restrict Protected to some heap types. (#6471)

* Restrict `Protected` to some heap types.

* Comment abut Protected usage.

* Remove Protected from crypto, use secrecy crate for existing uses.

* use a parse function

* fix error convert

* Rename and move secretY string function.

* std result

substrate/Cargo.lock

@@ -7089,6 +7089,15 @@ dependencies = [
  "untrusted",
 ]
 
+[[package]]
+name = "secrecy"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9182278ed645df3477a9c27bfee0621c621aa16f6972635f7f795dae3d81070f"
+dependencies = [
+ "zeroize",
+]
+
 [[package]]
 name = "security-framework"
 version = "0.4.2"
@@ -7616,6 +7625,7 @@ dependencies = [
  "rand_chacha 0.2.2",
  "regex",
  "schnorrkel",
+ "secrecy",
  "serde",
  "serde_json",
  "sha2",