feat: add quoting support to to_dict (#1052)

[clumsy]

See #1052

Test plan:
[x] all existing test cases pass

[x] add new test case

[x] test locally:

Given:

[component:dist.ddp]
script=test.py
env=
	NCCL_IB_HCA='=mlx5_0:1,mlx5_1:1';

Observe:

test/0 [7]:environ({...'NCCL_IB_HCA': '=mlx5_0:1,mlx5_1:1', ...})

[clumsy]

Please consider this PR, @kiukchung, @d4l3k, @tonykao8080 and sorry for using regex 🙂

[andywag]

Why use quotes instead of the more standard escape pattern?

[clumsy]

No particular preference besides being convenient to see the exact value without unescaping, @andywag - would be happy with any working solution.

Do you think an alternative mechanism is more desirable? Do you mean escaping like \=?

[andywag]

Yeah, I prefer the more standard escape like you mention but am fine with this since it's working.

[andywag]

lgtm

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