Public nodes can disable API auth. Always setting X-Algo-API-Token to an
empty string caused those requests to fail. Only send the header when
both the header name and token are non-empty.

Fixes #653.

Closes algorandfoundation/algorand-typescript-testing#145

Fail locally with the leftover token names instead of sending
unsubstituted TMPL_* integers to algod (ParseUint invalid syntax).

Closes #424.

Closes algorandfoundation/algokit-utils-ts#574

A logic signature authorizes a transaction with a program instead of a key. The
program either owns its own account, whose address is the hash of the program, or
is delegated by an account that signs it and spends from its own balance.

SignedTransaction gains an lsig field, so a logicsig-signed transaction now
survives a decode and re-encode instead of silently losing its authorization.

Delegation targets lmsig. Consensus v41 rejects the legacy msig field on a
LogicSig, because it hashed the bare program under the same domain separator a
single-key delegation uses, letting a member's subsignature be lifted out and
replayed as their own personal delegation. lmsig binds the multisig account
address into the signed bytes. The msig field is kept so historical transactions
decode, but nothing produces it.

The block template declared its own opaque lsig field beside the flattened
SignedTransaction, which would have shadowed the real one. Removed there and
added to both generator constructors; algod_client/tests/models.rs pins that a
logic signature reaches the flattened type, and lives outside src/ so it survives
regeneration.

The escrow address test uses the known program and address pair from the
js-algorand-sdk suite rather than a locally computed value.