Enable safe fallback when loading single values

[akaIDIOT]

• needs reviewer(s) to agree with the implementation
• needs changelog entry

[akaIDIOT]

Not sure this implementation is entirely kosher, thoughts welcome 🤔

This combined with calling it where singular values are expected does actually fairly transparently solve the issue.

[github-actions]

Comparing median (lower is better) metric of benchmarks between this PR's target (562ed1c) and the HEAD of this PR (4d54ee9):

	3.10	3.11	3.12	3.13	3.14	3.15	PyPy 3.10	PyPy 3.11
test_benchmark_get	+2%	-3%	-4%	+0%	-1%	+2%	-2%	+1%
test_benchmark_get_dotted	-1%	-1%	-0%	+2%	-2%	+4%	-3%	+0%
test_benchmark_getattr	+2%	-2%	-3%	+0%	-1%	+3%	+1%	+3%
test_benchmark_getitem	+2%	-2%	-3%	+1%	-2%	+2%	+1%	+2%
test_benchmark_getitem_dotted	-2%	-2%	+0%	+2%	-3%	-0%	-5%	-2%
test_benchmark_init_full_overlap	+2%	+3%	-1%	-1%	-2%	+0%	-2%	+1%
test_benchmark_init_no_overlap	+2%	+1%	-0%	-2%	-2%	-1%	+0%	+2%
test_benchmark_init_partial_overlap	+3%	+3%	-1%	-0%	-1%	+1%	-2%	+2%
test_benchmark_match_mapping	+2%	-1%	-4%	-0%	-1%	+2%	+1%	-0%
test_benchmark_reference_chain	-2%	+1%	-2%	-3%	+2%	+1%	-1%	+2%
test_benchmark_splat_args	+1%	+6%	+0%	-0%	+1%	+0%	+5%	+8%
test_benchmark_spread_kwargs	-2%	+2%	+1%	-1%	-1%	+4%	+2%	-0%

(This comment will be updated on subsequent pushes)

[akaIDIOT]

Changing this needs a test

[akaIDIOT]

Alternatively, we could so something like Format(strict=False), where the fallback type is always str. Less explicit, maybe easier to understand?