Improve deserialization docs (#2766)

Author: JoshMock

docs/observability.asciidoc

@@ -97,7 +97,7 @@ client.diagnostic.on('request', (err, result) => {
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 |`deserialization`
-a|Emitted before starting deserialization and decompression. If you want to measure this phase duration, you should measure the time elapsed between this event and `response`. _(This event might not be emitted in certain situations)_.
+a|Emitted before starting deserialization and decompression. If you want to measure this phase duration, you should measure the time elapsed between this event and `response`. This event might not be emitted in certain situations, like: when `asStream` is set to true; a response is terminated early due to content length being too large; or a response is terminated early by an `AbortController`.
 [source,js]
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 client.diagnostic.on('deserialization', (err, result) => {