fn: expand the ContextGuard and add tests #16873

Job	Run time
RPC and mobile compilation check	1m 41s
Sqlc check	2m 42s
check commits	8m 20s
cross compilation	30m 38s
lint code	4m 8s
sample configuration check	34s
run unit tests (btcd unit-cover)	19m 21s
check pinned dependencies (google.golang.org/grpc v1.59.0)	3s
run unit tests (unit tags="kvdb_etcd")	20m 42s
run ubuntu itests (btcd, backend=btcd cover=1)	29m 43s
check pinned dependencies (github.com/golang/protobuf v1.5.3)	4s
run unit tests (unit tags="kvdb_postgres")	20m 0s
run ubuntu itests (bitcoind, backend=bitcoind cover=1)	39m 5s
run unit tests (unit tags="kvdb_sqlite")	17m 46s
run ubuntu itests (bitcoind-notxindex, backend="bitcoind notxindex")	38m 27s
run unit tests (btcd unit-race)	39m 54s
run windows itest	7m 10s
run unit tests (unit-module)	1m 5s
run ubuntu itests (bitcoind-rpcpolling, backend="bitcoind rpcpolling" cover=1)	39m 10s
check release notes updated	4s
run macOS itest	53m 24s
run ubuntu itests (bitcoind-etcd, backend=bitcoind dbbackend=etcd)	53m 43s
run ubuntu itests (bitcoind-postgres, backend=bitcoind dbbackend=postgres)	1h 11m 42s
run ubuntu itests (bitcoind-sqlite, backend=bitcoind dbbackend=sqlite)	43m 1s
run ubuntu itests (bitcoind-postgres-nativesql, backend=bitcoind dbbackend=postgres nativesql=true)	1h 11m 17s
run ubuntu itests (bitcoind-sqlite-nativesql, backend=bitcoind dbbackend=sqlite nativesql=true)	42m 10s
run ubuntu itests (neutrino, backend=neutrino cover=1)	36m 27s
finish	5s
	11h 32m 26s

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