Define Pager (#620)

Signed-off-by: mramotar <mramotar@dropbox.com>

paging/core/src/commonMain/kotlin/org/mobilenativefoundation/paging/core/Pager.kt

@@ -0,0 +1,35 @@
+package org.mobilenativefoundation.paging.core
+
+import kotlinx.coroutines.flow.StateFlow
+
+/**
+ * [Pager] is responsible for coordinating the paging process and providing access to the paging state and data.
+ * This is the main entry point for the [org.mobilenativefoundation.paging] library.
+ *
+ * @param Id The type of the unique identifier for each item in the paged data.
+ * @param K The type of the key used for paging.
+ * @param P The type of the parameters associated with each page of data.
+ * @param D The type of the data items.
+ * @param E The type of errors that can occur during the paging process.
+ * @param A The type of custom actions that can be dispatched to modify the paging state.
+ */
+interface Pager<Id : Comparable<Id>, K : Any, P : Any, D : Any, E : Any, A : Any> {
+    /**
+     * The current paging state exposed as a [StateFlow].
+     * The paging state represents the current state of the paging data, including loaded pages, errors, and loading status.
+     * Observers can collect this flow to react to changes in the paging state.
+     */
+    val state: StateFlow<PagingState<Id, K, P, D, E>>
+
+    /**
+     * Dispatches a user-initiated [PagingAction] to modify the paging state.
+     *
+     * User actions can be dispatched to trigger specific behaviors or modifications to the paging state.
+     * The dispatched action will go through the configured [Middleware] chain and [Reducer] before updating the paging state.
+     * After updating the state, the dispatched action will launch each configured post-reducer [Effect].
+     *
+     * @param action The user-initiated [PagingAction] to dispatch.
+     */
+    fun dispatch(action: PagingAction.User<Id, K, P, D, E, A>)
+}
+