implements copy-on-write for staked-nodes (backport #19090) (#22507)

* implements copy-on-write for staked-nodes (#19090)

Bank::staked_nodes and Bank::epoch_staked_nodes redundantly clone
staked-nodes HashMap even though an immutable reference will suffice:
https://github.com/solana-labs/solana/blob/a9014cece/runtime/src/vote_account.rs#L77

This commit implements copy-on-write semantics for staked-nodes by
wrapping the underlying HashMap in Arc<...>.

(cherry picked from commit f302774cf7)

# Conflicts:
#	runtime/src/bank.rs
#	runtime/src/stakes.rs
#	runtime/src/vote_account.rs

* removes backport merge conflicts

Co-authored-by: behzad nouri <behzadnouri@gmail.com>

programs/bpf/Cargo.lock

@@ -1430,9 +1430,9 @@ dependencies = [
 
 [[package]]
 name = "itertools"
-version = "0.10.0"
+version = "0.10.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "37d572918e350e82412fe766d24b15e6682fb2ed2bbe018280caa810397cb319"
+checksum = "a9a9d19fa1e79b6215ff29b9d6880b706147f16e9b1dbb1e4e5947b5b02bc5e3"
 dependencies = [
  "either",
 ]
@@ -2764,7 +2764,7 @@ dependencies = [
  "bincode",
  "byteorder 1.3.4",
  "elf",
- "itertools 0.10.0",
+ "itertools 0.10.3",
  "log",
  "miow 0.2.2",
  "net2",
@@ -3501,7 +3501,7 @@ dependencies = [
  "dir-diff",
  "flate2",
  "fnv",
- "itertools 0.9.0",
+ "itertools 0.10.3",
  "lazy_static",
  "libc",
  "libloading",