* add FeeFields type
* use FeeFields with ::zero and try_into().unwrap()
* fixed tests
* avoid 0 accept_base_fee
* add aggregate_fee_fields method for transaction
* implement std::fmt::Display trait for FeeFields
* make base_fee argument non-optional in libtx::mod::tx_fee
* add global and thread local accept_fee_base; use to simplify tests
* set unusually high fee base for a change
* revert to optional base fee argument; default coming from either grin-{server,wallet}.toml
* remove optional base fee argument; can be set with global::set_local_accept_fee_base instead
* define constant global::DEFAULT_ACCEPT_FEE_BASE and set global value
* add Transaction::accept_fee() method and use
* Manual (de)ser impl on FeeFields
* fix comment bug
* Serialize FeeFields as int in tx
* allow feefields: u32:into() for tests
* try adding height args everywhere
* make FeeFields shift/fee methods height dependent
* prior to hf4 feefield testing
* rename selected fee_fields back to fee for serialization compatibility
* fix test_fee_fields test, merge conflict, and doctest use of obsolete fee_fields
* make accept_fee height dependent
* Accept any u64 in FeeFields deser
Co-authored-by: Jasper van der Maarel <j@sper.dev>
