feat: add plan builders (#73)

- add plan builders for read, project, filter, etc
- add simple builders for types

Author: tokoko

examples/builder_example.py

@@ -0,0 +1,138 @@
+from substrait.builders.plan import read_named_table, project, filter
+from substrait.builders.extended_expression import column, scalar_function, literal
+from substrait.builders.type import i64, boolean, struct, named_struct
+from substrait.extension_registry import ExtensionRegistry
+
+registry = ExtensionRegistry(load_default_extensions=True)
+
+ns = named_struct(
+    names=["id", "is_applicable"], 
+    struct=struct(
+        types=[
+            i64(nullable=False), 
+            boolean()
+        ]
+    )
+)
+
+table = read_named_table('example_table', ns)
+table = filter(table, expression=column('is_applicable'))
+table = filter(table, expression=scalar_function('functions_comparison.yaml', 'lt', column('id'), literal(100, i64())))
+table = project(table, expressions=[column('id')])
+
+print(table(registry))
+
+"""
+extension_uris {
+  extension_uri_anchor: 13
+  uri: "functions_comparison.yaml"
+}
+extensions {
+  extension_function {
+    extension_uri_reference: 13
+    function_anchor: 495
+    name: "lt"
+  }
+}
+relations {
+  root {
+    input {
+      project {
+        common {
+          emit {
+            output_mapping: 2
+          }
+        }
+        input {
+          filter {
+            input {
+              filter {
+                input {
+                  read {
+                    common {
+                      direct {
+                      }
+                    }
+                    base_schema {
+                      names: "id"
+                      names: "is_applicable"
+                      struct {
+                        types {
+                          i64 {
+                            nullability: NULLABILITY_REQUIRED
+                          }
+                        }
+                        types {
+                          bool {
+                            nullability: NULLABILITY_NULLABLE
+                          }
+                        }
+                        nullability: NULLABILITY_NULLABLE
+                      }
+                    }
+                    named_table {
+                      names: "example_table"
+                    }
+                  }
+                }
+                condition {
+                  selection {
+                    direct_reference {
+                      struct_field {
+                        field: 1
+                      }
+                    }
+                    root_reference {
+                    }
+                  }
+                }
+              }
+            }
+            condition {
+              scalar_function {
+                function_reference: 495
+                output_type {
+                  bool {
+                    nullability: NULLABILITY_NULLABLE
+                  }
+                }
+                arguments {
+                  value {
+                    selection {
+                      direct_reference {
+                        struct_field {
+                        }
+                      }
+                      root_reference {
+                      }
+                    }
+                  }
+                }
+                arguments {
+                  value {
+                    literal {
+                      i64: 100
+                      nullable: true
+                    }
+                  }
+                }
+              }
+            }
+          }
+        }
+        expressions {
+          selection {
+            direct_reference {
+              struct_field {
+              }
+            }
+            root_reference {
+            }
+          }
+        }
+      }
+    }
+    names: "id"
+  }
+}
+"""