Add `link` to filehandler and its associated test #232

Job	Run time
Install wxflow and run tests with pytests (3.8)	27s
Install wxflow and run tests with pytests (3.9)	26s
Install wxflow and run tests with pytests (3.10)	20s
Install wxflow and run tests with pytests (3.11)	18s
Install wxflow and run tests with pytests (3.12)	24s
Install wxflow and run tests with pytests (3.13)	21s
	2m 16s

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