Implement NIP-19 bech32-encoded private and public keys

https://github.com/nostr-protocol/nips/blob/master/19.md

sig/vendor/bech32/nostr/entity.rbs

@@ -0,0 +1,41 @@
+# Added only to satisfy the Steep requirements. Not 100% reliable.
+module Bech32
+  module Nostr
+    class BareEntity
+      attr_reader hrp: untyped
+      attr_reader data: untyped
+
+      def initialize: (untyped hrp, untyped data) -> void
+      def encode: -> untyped
+    end
+
+    class TLVEntry
+      attr_reader type: (Float | Integer | String)?
+      attr_reader label: String?
+      attr_reader value: (Float | Integer | String)?
+
+      def initialize: ((Float | Integer | String)? `type`, (Float | Integer | String)? value, ?String? label) -> void
+      def to_payload: -> String
+      def to_s: -> String
+
+      private
+
+      def hex_string?: ((Float | Integer | String)? str) -> bool
+    end
+
+    class TLVEntity
+      TYPE_SPECIAL: Integer
+      TYPE_RELAY: Integer
+      TYPE_AUTHOR: Integer
+      TYPE_KIND: Integer
+      TYPES: [Integer, Integer, Integer, Integer]
+
+      attr_reader hrp: untyped
+      attr_reader entries: Array[TLVEntry]
+
+      def initialize: (untyped hrp, Array[TLVEntry] entries) -> void
+      def self.parse: (untyped hrp, untyped data) -> TLVEntity
+      def encode: -> untyped
+    end
+  end
+end

sig/vendor/bech32/nostr/nip19.rbs

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+# Added only to satisfy the Steep requirements. Not 100% reliable.
+module Bech32
+  module Nostr
+    module NIP19
+      HRP_PUBKEY: String
+      HRP_PRIVATE_KEY: String
+      HRP_NOTE_ID: String
+      HRP_PROFILE: String
+      HRP_EVENT: String
+      HRP_RELAY: String
+      HRP_EVENT_COORDINATE: String
+      BARE_PREFIXES: [String, String, String]
+      TLV_PREFIXES: [String, String, String, String]
+      ALL_PREFIXES: Array[String]
+
+      def decode: (untyped string) -> untyped
+      def self.decode: (untyped string) -> untyped
+    end
+  end
+end

sig/vendor/bech32/segwit_addr.rbs

@@ -0,0 +1,21 @@
+# Added only to satisfy the Steep requirements. Not 100% reliable.
+module Bech32
+  class SegwitAddr
+    HRP_MAINNET: String
+    HRP_TESTNET: String
+    HRP_REGTEST: String
+
+    attr_accessor hrp: String
+    attr_accessor ver: (Float | Integer | String)?
+    attr_accessor prog: Array[(Float | Integer | String)?]
+
+    def initialize: (?nil addr) -> void
+    def to_script_pubkey: -> ((Float | Integer | String)?)
+    def script_pubkey=: (untyped script_pubkey) -> (Array[(Float | Integer | String)?])
+    def addr: -> untyped
+
+    private
+
+    def parse_addr: (untyped addr) -> nil
+  end
+end