various: add golangci-lint, fix issues (#7905)

This adds an initial and intentionally minimal configuration for
golang-ci, fixes the issues reported, and adds a GitHub Action to check
new pull requests against this linter configuration.

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I8f38fbc315836a19a094d0d3e986758b9313f163

tka/tka.go

@@ -359,7 +359,7 @@ func computeActiveAncestor(storage Chonk, chains []chain) (AUMHash, error) {
 
 	if len(ancestors) == 1 {
 		// There's only one. DOPE.
-		for k, _ := range ancestors {
+		for k := range ancestors {
 			return k, nil
 		}
 	}
@@ -390,7 +390,7 @@ func computeActiveAncestor(storage Chonk, chains []chain) (AUMHash, error) {
 //     formerly (in a previous run) part of the chain.
 //  3. Compute the state of the state machine at this ancestor. This is
 //     needed for fast-forward, as each update operates on the state of
-//     the update preceeding it.
+//     the update preceding it.
 //  4. Iteratively apply updates till we reach head ('fast forward').
 func computeActiveChain(storage Chonk, lastKnownOldest *AUMHash, maxIter int) (chain, error) {
 	chains, err := computeChainCandidates(storage, lastKnownOldest, maxIter)