psbt: make PsbtInputSatisfier internals private

We don't need access to the internals anywhere, and this is just a POD
type with two Copy objects inside so the user can just keep them around
after construction if they need access.

Add an accessor for the PSBT anyway since it might be convenient.

Making these fields private does not break compilation at all.

Author: apoelstra

src/psbt/mod.rs

@@ -243,16 +243,19 @@ impl From<bitcoin::key::FromSliceError> for InputError {
 /// is more than number of inputs in pbst
 pub struct PsbtInputSatisfier<'psbt> {
     /// pbst
-    pub psbt: &'psbt Psbt,
+    psbt: &'psbt Psbt,
     /// input index
-    pub index: usize,
+    index: usize,
 }
 
 impl<'psbt> PsbtInputSatisfier<'psbt> {
     /// create a new PsbtInputsatisfier from
     /// psbt and index
     pub fn new(psbt: &'psbt Psbt, index: usize) -> Self { Self { psbt, index } }
 
+    /// Accessor for the PSBT this satisfier is associated with.
+    pub fn psbt(&self) -> &'psbt Psbt { self.psbt }
+
     /// Accessor for the input this satisfier is associated with.
     pub fn psbt_input(&self) -> &psbt::Input { &self.psbt.inputs[self.index] }
 }