DbSvr: Update snmp

[FreddieAkeroyd]

Description of work

Update snmp libraries - see ISISComputingGroup/IBEX#8958

Acceptance criteria

Unit tests pass and instrument starts with moxa details

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Code Review

• Is the code of an acceptable quality?
• Has the author taken into account the multi-threaded nature of the code?
• Have the changes been recorded appropriately in a PR for release notes?
• Has the manual system tests spreadsheet been updated?

Functional Tests

• Do changes function as described? Add comments below that describe the tests performed.

Final steps

• Reviewer has updated the submodule in the main EPICS repo? See Reviewing work for the subModules of EPICS in the Git workflow page for details.
• Reviewer has merged the associated PR for the release notes

[Tom-Willemsen]

Note: this is tied to ISISComputingGroup/uktena#30 and should be merged at the same time

[Chsudeepta]

I remember pysnmp-lextudio and snmpsim-lextudio were probably required for Lyndy. Are these not used anymore?