fix regression where COLD_PW can no longer be passed with env vars co…

Bug

Description of the Change

Apparently, in the context of python it was possible to set a env var with hyphen in it. Which makes change introduced by https://github.com/opentensor/bittensor/pull/1949 a breaking one which is not acceptable as it was introduced in minor version of bittensor, hence breaking semver contract.

This PR makes sure we support proper env variable names, while also not breaking users that used hyphens within the env var name.

See https://discord.com/channels/1120750674595024897/1242999357436071956/1284309400751964271 for more context.

Alternate Designs

Ignore the regression, but that conflicts with semver versioning and further discourages keeping with the latest bittensor version.

Possible Drawbacks

Not forcing users to migrate asap.

Verification Process

Unit test

Release Notes

fix regression which broke passing passcode through env var with hyphen, e.g. BT_COLD_PW_My-Wallet3=pw. Please note this form is deprecated, and one should use BT_COLD_PW_My_Wallet3=pw instead.

opentensor / bittensor