fix: excessive hash creation on context attr merging

[robertlaurin]

Fixes the ordering of attribute merging in some places, switches to using merge! to avoid creating an additional hash on merge.

[arielvalentin]

I wonder if there is a linter we could leverage for this 🤔

[robertlaurin]

I wonder if there is a linter we could leverage for this

Yeah I thought about it too, but I don't know how we could make it nuanced enough, we don't also want to use it where we want to preserve the thing that is getting merged.

Like here for example, I think we want to preserve the original hash as we potentially nest various client contexts

opentelemetry-ruby/common/lib/opentelemetry/common/http/client_context.rb

Lines 33 to 36 in df9bbb0

	def context_with_attributes(attributes_hash, parent_context: Context.current)
	attributes_hash = attributes(parent_context).merge(attributes_hash)
	parent_context.set_value(CURRENT_ATTRIBUTES_HASH, attributes_hash)
	end

Also we do not want to accidentally .merge! on the client context attributes as that could have buggy side effects.