*: move PreHeader() and Header() getters to Context

These fields are a part of dBFT context, they should be accessible via
those methods that expose Context to the user.

Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>

CHANGELOG.md

@@ -8,6 +8,7 @@ New features:
 
 Behaviour changes:
  * adjust behaviour of ProcessPreBlock callback (#129)
+ * (*DBFT).Header() and (*DBFT).PreHeader() are moved to (*Context) receiver (#133)
 
 Improvements:
  * minimum required Go version is 1.22 (#122, #126)

context.go

@@ -214,6 +214,18 @@ func (c *Context[H]) MoreThanFNodesCommittedOrLost() bool {
 	return c.CountCommitted()+c.CountFailed() > c.F()
 }
 
+// Header returns current header from context. May be nil in case if no
+// header is constructed yet. Do not change the resulting header.
+func (c *Context[H]) Header() Block[H] {
+	return c.header
+}
+
+// PreHeader returns current preHeader from context. May be nil in case if no
+// preHeader is constructed yet. Do not change the resulting preHeader.
+func (c *Context[H]) PreHeader() PreBlock[H] {
+	return c.preHeader
+}
+
 // PreBlock returns current PreBlock from context. May be nil in case if no
 // PreBlock is constructed yet (even if PreHeader is already constructed).
 // External changes in the PreBlock will be seen by dBFT.

dbft.go

@@ -703,15 +703,3 @@ func (d *DBFT[H]) extendTimer(count int) {
 		d.Timer.Extend(time.Duration(count) * d.SecondsPerBlock / time.Duration(d.M()))
 	}
 }
-
-// Header returns current header from context. May be nil in case if no
-// header is constructed yet. Do not change the resulting header.
-func (d *DBFT[H]) Header() Block[H] {
-	return d.header
-}
-
-// PreHeader returns current preHeader from context. May be nil in case if no
-// preHeader is constructed yet. Do not change the resulting preHeader.
-func (d *DBFT[H]) PreHeader() PreBlock[H] {
-	return d.preHeader
-}