Code coverage example for a simple Anchor app

[procdump]

Summary

• Adds a code coverage example demonstrating how to generate coverage reports for Anchor programs using Surfpool's register-tracing feature and sbpf-coverage
• Based on LimeChain/simple_anchor_app
• Updates main README and anchor README with the new example

Related

• Requires txtx/surfpool#496 (Allow building surfpool with LiteSVM's register-tracing feature)

[procdump]

If everything looks good for solana-foundation/surfpool#573, solana-foundation/surfpool#574, solana-foundation/txtx#399 and they get merged the steps in this example can be narrowed down to:

# build as usual, actually the IDL is only needed
anchor build
# produce a program that has debug info
RUSTFLAGS="-Copt-level=0 -C strip=none -C debuginfo=2" cargo build-sbf --tools-version v1.53 --arch v1 --debug
# start surfpool
SBF_TRACE_DIR=$PWD/target/sbf_trace_dir surfpool start --artifacts-path ./target/deploy/debug --watch
# run the test
anchor test --skip-local-validator --skip-build --skip-deploy
# get code coverage
sbpf-coverage --src-path=$PWD/programs/simple_anchor_app/src \
		--sbf-path=$PWD/target/deploy/debug \
		--sbf-trace-dir=$PWD/target/sbf_trace_dir