This changes the SimultaneousRequests test to send the requests from the same
connection, as it doesn't really make sense to test whether a node can respond
to two requests with different request IDs from separate connections.

With the update to a newer AppVeyor build image, creating the Windows
installer no longer worked because of a string quoting error in EnvVarUpdate.nsh.

This applies the fix recommended in https://stackoverflow.com/questions/62081765.

This fixes a regression introduced in #22804.

This updates go.mod for the addition of golang.org/x/sync.

This PR cleans up the CI build system and fixes a couple of issues.

- The go tool launcher code has been moved to internal/build. With the new
  toolchain functions, the environment of the host Go (i.e. the one that built
  ci.go) and the target Go (i.e. the toolchain downloaded by -dlgo) are isolated
  more strictly. This is important to make cross compilation and -dlgo work
  correctly in more cases.
- The -dlgo option now skips the download and uses the host Go if the running Go
  version matches dlgoVersion exactly.
- The 'test' command now supports -dlgo, -cc and -arch. Running unit tests with
  foreign GOARCH is occasionally useful. For example, it can be used to run
  32-bit tests on Windows. It can also be used to run darwin/amd64 tests on
  darwin/arm64 using Rosetta 2.
- The 'aar', 'xcode' and 'xgo' commands now use a slightly different method to
  install external tools. They previously used `go get`, but this comes with the
  annoying side effect of modifying go.mod. They now use `go install` instead,
  which is the recommended way of installing tools without modifying the local
  module.
- The old build warning about outdated Go version has been removed because we're
  much better at keeping backwards compatibility now.

This removes auto-configuration of the snap.*.ethdisco.net DNS discovery tree.
Since measurements have shown that > 75% of nodes in all.*.ethdisco.net support
snap, we have decided to retire the dedicated index for snap and just use the eth
tree instead.

The dial iterators of eth and snap now use the same DNS tree in the default configuration,
so both iterators should use the same DNS discovery client instance. This ensures that
the record cache and rate limit are shared. Records will not be requested multiple times.

While testing the change, I noticed that duplicate DNS requests do happen even
when the client instance is shared. This is because the two iterators request the tree
root, link tree root, and first levels of the tree in lockstep. To avoid this problem, the
change also adds a singleflight.Group instance in the client. When one iterator
attempts to resolve an entry which is already being resolved, the singleflight object
waits for the existing resolve call to finish and returns the entry to both places.

eth: don't print db upgrade warning on db init

core: remove old conversion to shuffle leveldb blocks into ancients

* params: remove dependency on crypto

Package params should not depend on package crypto because building
crypto requires cgo.

Since build/ci.go needs package params to get the go-ethereum version
number, C code must be compiled in order to run the build tool, which is
annoying for certain cross-compilation setups.

* params: add SectionHead

* Fix interpreter comment

* Fix comment

Do not keep separate flag for "max code size exceeded" case, but instead
assign appropriate error for it sooner.

This PR fixes a couple of issues in the eth test suite that caused flakiness when run in the CI.

eth/protocols/snap: use storage batch, not account batch in st task

core, eth: abort snapshot generation on snap sync and resume later

eth: restore eth_hashrate API endpoint

core, eth, ethdb, trie: simplify range proofs

* trie: add benchmark for proofless range

* trie: remove unused returns + use stacktrie

eth/protocols/snap: lower the packet size to avoid overloading link