…ding

Remove S, P generic parameters from Sender, SendTxs, and TxGenerator by
introducing SerializedTx/BuiltTransactions types that pre-serialize
transactions in the builder. Externalize context building from individual
builders to TxGenerator::build_txs via relevant_wallet_seeds().

- Restructure builders into common/ + version wrappers (ledger_8.rs,
  ledger_7.rs) using ledger_helpers_local module alias for explicit
  version-specific imports
- build_fork_aware_context and build_context_with_cache now return
  Result<_, ContextNotLedger8Error> instead of panicking
- Update all callers to propagate errors with ?
- Delete unused fork_aware_block_data.rs

Builders now dispatch to the correct ledger version at construction time
via Builder::to_versioned_builder(). Cross-version type conversion uses
raw bytes for hash types, bech32 for addresses, and try_from for seeds.
Version-local tx serialization replaces the ledger-8-bound
DeserializedTransactionsWithContext. contract_custom is excluded from
ledger 7 as EncodedOutputInfo only implements ledger 8 BuildOutput.

Pass --build to docker compose up so that locally-built images
(e.g. contract-compiler) are rebuilt when their Dockerfile changes,
preventing stale images from being reused.

local-env uses a different chain network id to the network id encoded
in the ledger transactions - this is non-standard, but the toolkit should
not break because of this.

The top-level fork/ module mixed concerns (commands, builders,
transactions) under a single umbrella. Move version-specific command
implementations into commands/fork/ where they colocate with the
dispatch logic, and consolidate the shared from_serde_tx into the
existing tx_generator builders via a transactions.rs module. The
duplicate fork/builders/ is removed since tx_generator/builder/builders/
already provides the same functionality.

Replace the manual PartialEq/Eq/Ord/PartialOrd impls that only compared
tblock_secs with derived PartialEq/Eq. The single sort call site now
uses sort_by_key instead.