BOLT 12 messages are limited to a range of TLV record types. Refactor
decode_tlv_stream into a decode_tlv_stream_range macro for limiting
which types are parsed. Requires a SeekReadable trait for rewinding when
a type outside of the range is seen. This allows for composing TLV
streams of different ranges.
Updates offer parsing accordingly and adds a test demonstrating failure
if a type outside of the range is included.
Add common bech32 parsing for BOLT 12 messages. The encoding is similar
to bech32 only without a checksum and with support for continuing
messages across multiple parts.
Messages implementing Bech32Encode are parsed into a TLV stream, which
is converted to the desired message content while performing semantic
checks. Checking after conversion allows for more elaborate checks of
data composed of multiple TLV records and for more meaningful error
messages.
The parsed bytes are also saved to allow creating messages with mirrored
data, even if TLV records are unknown.
Add a builder for creating offers given a required description and
node_id. Other settings are optional and duplicative settings will
override previous settings for non-Vec fields.
Define an interface for BOLT 12 `offer` messages. The underlying format
consists of the original bytes and the parsed contents.
The bytes are later needed when constructing an `invoice_request`
message. This is because it must mirror all the `offer` TLV records,
including unknown ones, which aren't represented in the contents.
The contents will be used in `invoice_request` messages to avoid
duplication. Some fields while required in a typical user-pays-merchant
flow may not be necessary in the merchant-pays-user flow (i.e., refund).
