Unify Property Naming Convention to `snake_case` for Consistency

[jneums]

Hi @skilesare,

First off, thank you for the excellent work on the ICRC-127 spec. The generic bounty system is a fantastic and much-needed addition to the IC ecosystem.

While implementing a client based on the draft, I noticed some minor inconsistencies in the naming convention for property names within the Candid type definitions. The spec uses a mix of snake_case and camelCase.

Adopting a single, consistent convention would improve clarity for implementers and make the standard feel even more polished. Given the prevalence of snake_case in many other ICRC standards, I'd like to suggest unifying all property names to follow that pattern.

Here is a list of the specific instances I found:

Type Definition	Current camelCase Property	Suggested snake_case Property
RunBountyResult	trxId	trx_id
ClaimRecord	claimId	claim_id
ClaimRecord	timeSubmitted	time_submitted
Bounty	bountyMetadata	bounty_metadata
CreateBountyResult.Ok	bountyId	bounty_id
CreateBountyResult.Ok	trxId	trx_id
BountySubmissionResult.Ok	claimId	claim_id

Aligning these properties with snake_case would make the entire spec internally consistent.

Thanks again for your effort on this important standard. Hope this feedback is helpful