CLI: dynamic signing reboot (#8384)

* Add keypair_util_from_path helper

* Cli: impl config.keypair as a trait object

* SDK: Add Debug and PartialEq for dyn Signer

* ClapUtils: Arg parsing from pubkey+signers to Presigner

* Impl Signers for &dyn Signer collections

* CLI: Add helper for getting signers from args

* CLI: Replace SigningAuthority with Signer trait-objs

* CLI: Drop disused signers command field

* CLI: Drop redundant tests

* Add clap validator that handles all current signer types

* clap_utils: Factor Presigner resolution to helper

* SDK: `From` for boxing Signer implementors to trait objects

* SDK: Derive `Clone` for `Presigner`

* Remove panic

* Cli: dedup signers in transfer for remote-wallet ergonomics

* Update docs vis-a-vis ASK changes

* Cli: update transaction types to use new dynamic-signer methods

* CLI: Fix tests No. 1

what to do about write_keypair outstanding

* Work around `CliConfig`'s signer not necessarily being a `Keypair`

* CLI: Fix tests No. 2

* Remove unused arg

* Remove unused methods

* Move offline arg constants upstream

* Make cli signing fallible

Co-authored-by: Trent Nelson <trent.a.b.nelson@gmail.com>

clap-utils/src/offline.rs

@@ -0,0 +1,19 @@
+use crate::ArgConstant;
+
+pub const BLOCKHASH_ARG: ArgConstant<'static> = ArgConstant {
+    name: "blockhash",
+    long: "blockhash",
+    help: "Use the supplied blockhash",
+};
+
+pub const SIGN_ONLY_ARG: ArgConstant<'static> = ArgConstant {
+    name: "sign_only",
+    long: "sign-only",
+    help: "Sign the transaction offline",
+};
+
+pub const SIGNER_ARG: ArgConstant<'static> = ArgConstant {
+    name: "signer",
+    long: "signer",
+    help: "Provide a public-key/signature pair for the transaction",
+};