Upgrades to node & base images for node and python

[davidwilby]

Maintenance has ended for v14 and v18 is the current LTS version of node.

[github-actions]

Jest Coverage

File	% Stmts	% Branch	% Funcs	% Lines	Uncovered Line #s
All files	86.66	85.45	53.33	86.66

File	% Stmts	% Branch	% Funcs	% Lines	Uncovered Line #s
All files	86.66	85.45	53.33	86.66
_jrpc	94.04	91.66	83.33	94.04
_ index.js	94.04	91.66	83.33	94.04	29-30,38-40
_utils	83.98	83.72	33.33	83.98
_ annotations.js	97.72	73.91	100	97.72	35-36
_ dict.js	88.88	83.33	100	88.88	3-4
_ index.js	73.6	100	14.28	73.6	9-17,28-29,43-53,64-65,76-82,93-94

[ianroberts]

LGTM now, I guess rebase #356 once this has merged.

[davidwilby]

LGTM now, I guess rebase #356 once this has merged.

That's the plan! Thanks!