Improve error messages in stfn

[dapplion]

Motivation

Minor tweaks on error messages

Description

• Use a single string interpolation instead of many
• Fix typos
• Stringify checkpoints properly

[codeclimate]

Code Climate has analyzed commit 4d2fbbf and detected 2 issues on this pull request.

Here's the issue category breakdown:

Category	Count
Duplication	2

View more on Code Climate.

[github-actions]

Performance Report

✔️ no performance regression detected

Full benchmark results

Benchmark suite	Current: ce41cdc	Previous: c09ea9a	Ratio
getCommitteeAssignments - req 1000 vs - 250000 vc	7.8425 ms/op	9.2084 ms/op	0.85
processBlock altair 250000 vs - 7PWei - maxed ops	381.53 ms/op	563.59 ms/op	0.68
processBlock altair 250000 vs - 7PWei - average	133.09 ms/op	220.05 ms/op	0.60
epoch altair - 250000 vs - 7PWei - processInactivityUpdates	2.0532 s/op	2.6754 s/op	0.77
epoch altair - 250000 vs - 7PWei - processRewardsAndPenalties	906.36 ms/op	1.1298 s/op	0.80
epoch altair - 250000 vs - 7PWei - processParticipationFlagUpdates	462.42 ms/op	578.71 ms/op	0.80
processBlock phase0 250000 vs - 7PWei - maxed ops	157.66 ms/op	240.26 ms/op	0.66
processBlock phase0 250000 vs - 7PWei - average	24.721 ms/op	30.951 ms/op	0.80
epoch phase0 - 250000 vs - 7PWei - beforeProcessEpoch	1.4425 s/op	2.0031 s/op	0.72
epoch phase0 - 250000 vs - 7PWei - processRewardsAndPenalties	707.23 ms/op	918.98 ms/op	0.77
epoch phase0 - 250000 vs - 7PWei - processEffectiveBalanceUpdates	102.72 ms/op	135.53 ms/op	0.76
getAttestationDeltas - 250000 vs - 7PWei	102.28 ms/op	124.54 ms/op	0.82
processSlots - 250000 vs - 7PWei - 32 empty slots	2.8116 s/op	3.6104 s/op	0.78
shuffle list - 16384 els	25.314 ms/op	30.941 ms/op	0.82
shuffle list - 250000 els	250.38 ms/op	298.32 ms/op	0.84
getPubkeys - persistent - req 1000 vs - 250000 vc	17.475 us/op	20.070 us/op	0.87
BLS verify - blst-native	1.8576 ms/op	2.3405 ms/op	0.79
BLS verifyMultipleSignatures 3 - blst-native	3.8091 ms/op	4.8100 ms/op	0.79
BLS verifyMultipleSignatures 8 - blst-native	8.1979 ms/op	10.355 ms/op	0.79
BLS verifyMultipleSignatures 32 - blst-native	29.823 ms/op	37.961 ms/op	0.79
BLS aggregatePubkeys 32 - blst-native	40.492 us/op	78.616 us/op	0.52
BLS aggregatePubkeys 128 - blst-native	155.93 us/op	210.14 us/op	0.74
getAttestationsForBlock	73.608 ms/op	89.045 ms/op	0.83
validate gossip signedAggregateAndProof - struct	4.4937 ms/op	5.7115 ms/op	0.79
validate gossip signedAggregateAndProof - treeBacked	4.4562 ms/op	5.6947 ms/op	0.78
validate gossip attestation - struct	2.0957 ms/op	2.6666 ms/op	0.79
validate gossip attestation - treeBacked	2.1286 ms/op	2.6806 ms/op	0.79

by benchmarkbot/action