fix: EnvHelper unusable if error occurs during initialisation

[cecheta]

Purpose

• If an error occurs during env helper initialisation, the helper remains in a non-working state until the app restarts. This PR fixes this, so the env helper is only saved if it is created without any errors

Does this introduce a breaking change?

• [ ] Yes
• [x] No

[github-actions[bot]]

Coverage Report •

File	Stmts	Miss	Cover	Missing
code/backend/batch/utilities/helpers
env_helper.py	135	10	92%	223, 228–229, 232–234, 246, 250–252
TOTAL	2428	672	72%

Tests	Skipped	Failures	Errors	Time
206	0 :zzz:	0 :x:	0 :fire:	12.606s :stopwatch:

[ross-p-smith]

Not for this PR - but wonder whether the @functools.cache would be simpler than the lock

[cecheta]

Not for this PR - but wonder whether the @functools.cache would be simpler than the lock

From what I quickly saw online, there could be multiple threads trying to create EnvHelpers at the same time during startup unless we use a lock

I don't think that would break the application, but I guess it wouldn't be a true singleton