Using the tlv_stream macro without a type needing a reference results in
a compilation error because of an unused lifetime parameter. To avoid
this, add an optional lifetime parameter to the macro. This allows for
experimental TLVs, which will be empty initially, and TLVs of entirely
primitive types.

TlvRecord has a few fields, but comparing only the record_bytes is
sufficient for equality since the other fields are initialized from it.
Remove the Eq and PartialEq derives as they compare these other fields.

When constructing UnsignedInvoiceRequest or UnsignedBolt12Invoice, use a
separate field for experimental TLV bytes. This allows for properly
inserting the signature TLVs before the experimental TLVs when signing.

Add a utility function for iterating over Offer TLV records contained in
any valid TLV stream bytes. Using a common function ensures that
experimental TLV records are included once they are supported.

Passing bytes directly to InvoiceContents::verify improves readability
as then a TlvStream for each TLV record range can be created from the
bytes instead of needing to clone the TlvStream upfront. In an upcoming
commit, the experimental TLV record range will utilize this.

Upcoming commits will allow parsing BOLT12 messages that include TLV
records in the experimental range. Include these ranges when verifying
messages since they will be included in the message bytes.

The BOLT12 spec defines an experimental TLV range that are allowed in
offer messages. Allow this range when parsing an offer and include those
bytes in any invoice requests. Also include those bytes when computing
an OfferId and verifying that an InvoiceRequest is for a valid Offer.

Offer metadata is generated from the offer TLVs and should included
those in the experimental range. When verifying invoice request and
invoice messages, these TLVs must be included. Similarly, OfferId
construction should included these TLVs as well. Modify the BOLT12
verification tests to cover these TLVs.

The BOLT12 spec defines an experimental TLV range that are allowed in
invoice_request messages. Allow this range when parsing an invoice
request and include those bytes in any invoice. Also include those bytes
when verifying that a Bolt12Invoice is for a valid InvoiceRequest.

Payer metadata is generated from the invreq TLVs and should included
those in the experimental range. When verifying invoice messages, these
TLVs must be included. Modify the BOLT12 verification tests to cover
them.

The BOLT12 spec defines an experimental TLV range that is allowed in
offer and invoice_request messages. The remaining TLV-space is for
experimental use in invoice messages. Allow this range when parsing an
invoice and include it when signing one.