fix: sanitize event observer strings #2994

Job	Run time
lint	1m 19s
test-rosetta (rosetta-cli-data)	2m 17s
test-rosetta (rosetta)	3m 17s
test-rosetta (rosetta-construction)	2m 26s
test (btc-faucet)	1m 45s
test-snp	1m 47s
test (api)	11m 7s
test-2_5 (pox-4-btc-address-formats)	2m 15s
test-2_5 (faucet-stx)	1m 48s
test-rosetta (rosetta-cli-construction)	3m 1s
test-2_5 (block-zero-handling)	1m 44s
test (event-replay)	2m 7s
test-2_5 (pox-4-delegate-revoked-stacking)	2m 13s
test (bns-e2e)	7m 34s
test-2_5 (pox-4-delegate-aggregation)	2m 20s
test (bns)	3m 33s
test-2_5 (pox-4-delegate-stacking)	1m 42s
test-2_5 (pox-4-rosetta-btc-addr-types)	5m 27s
test (rpc)	1m 49s
test-2_5 (pox-4-burnchain-stack-stx)	1m 48s
test-2_5 (pox-4-rosetta-cycle-phases)	1m 24s
test-2_5 (pox-4-rosetta-segwit)	1m 51s
test-2_5 (pox-4-stack-extend-increase)	2m 28s
test-2_5 (pox-4-burnchain-delegate-stx)	1m 45s
build-publish	2m 45s
	1h 11m 32s

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