Backport Core burn from coreum repo

[TxCorpi0x]

Description

Backport PR#1173 from coreum.

This pull request adds support for burning the governance (bond) denom (such as core, testcore, or devcore) via the AssetFT module, in addition to existing AssetFT tokens. The changes include updating the keeper logic to allow this behavior, relaxing CLI and message validation, and adding comprehensive tests for both successful and failure scenarios when burning governance denoms.

Governance denom burn support:

• Updated the Keeper.Burn method to allow burning the governance/bond denom without requiring an AssetFT token definition, using the staking module to dynamically determine the bond denom. Burning is only allowed if the coins are not locked or restricted.
• Relaxed MsgBurn.ValidateBasic to skip AssetFT-specific denom validation, so governance denoms (like udevcore) can be burned; actual validation is deferred to the keeper.

CLI and documentation improvements:

• Enhanced the burn CLI command (CmdTxBurn) to document and support burning the governance/bond denom, with updated help text and usage examples.

Testing:

• Added integration and CLI tests to verify burning the governance denom works as intended, including supply and balance checks. [1] [2]
• Added extensive keeper unit tests covering successful burns, insufficient balance, zero/negative amounts, invalid denoms (IBC/random), module accounts, and locked coins for the governance denom.

Reviewers checklist:

• Try to write more meaningful comments with clear actions to be taken.
• Nit-picking should be unblocking. Focus on core issues.

Authors checklist

• Provide a concise and meaningful description
• Review the code yourself first, before making the PR.
• Annotate your PR in places that require explanation.
• Think and try to split the PR to smaller PR if it is big.

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This change is 

[miladz68]

@miladz68 reviewed 6 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @masihyeganeh, @metalarm10, and @ysv).

[masihyeganeh]

@masihyeganeh reviewed 6 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @metalarm10 and @ysv).

[masihyeganeh]

@masihyeganeh reviewed 2 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @metalarm10 and @ysv).

[miladz68]

@miladz68 reviewed 5 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on metalarm10 and ysv).