rpcserver: add decimal display to asset stats rpc

[jamaljsr]

In Terminal, we'd like to display the asset supply value with the decimal point based on the decimal_display included in the metadata. We use the QueryAssetStats REST endpoint to fetch assets from the universe server. Currently, the decimal display isn't included in the response.

This PR adds this field to each asset in the response if it was specified in the metadata when minting. I've tested with grouped & non-grouped assets, with and without a decimal_display set.

Here's what the updated response looks like:

{
    "asset_stats": [
        {
            "group_key": "",
            "group_supply": "0",
            "group_anchor": null,
            "asset": {
                "asset_id": "4b69c0f4aeb49ffc22822eb2c26590cedcf6900e6a72bcabbdbc9353f2709554",
                "genesis_point": "dea7f9185efb9554c149516956c0adb3fe8041dbcfead0852212f7d4622166d3:1",
                "total_supply": "1000000",
                "asset_name": "NoGroup",
                "asset_type": "NORMAL",
                "genesis_height": 329,
                "genesis_timestamp": "1748353581",
                "anchor_point": "9da69d2096225bb8ff8220ee1c05fa381e0654743bebb1c31f23c73d5894d9a5:0",
                "decimal_display": 3
            },
            "total_syncs": "0",
            "total_proofs": "1"
        },
        {
            "group_key": "03f54ee69f2ef8caaf7618d334a23c4f141ca0d275943a49fceeeba4dfe84545e5",
            "group_supply": "600000",
            "group_anchor": {
                "asset_id": "4c9ce145d903d303d4d2da125f5cf7a95bf874db3db76188c5e049c4c1a5e2a0",
                "genesis_point": "47e19c099260f609b7a5d4f5beb16df109098ee78714e07330d9e6f6e5b04dd8:1",
                "total_supply": "100000",
                "asset_name": "WithGroup",
                "asset_type": "NORMAL",
                "genesis_height": 303,
                "genesis_timestamp": "1748351609",
                "anchor_point": "052627e9b1da0f79a539c03aaff984ffe171a5df4cf55d8cef337b81d3054b46:0",
                "decimal_display": 2
            },
            "asset": null,
            "total_syncs": "0",
            "total_proofs": "3"
        },
        {
            "group_key": "",
            "group_supply": "0",
            "group_anchor": null,
            "asset": {
                "asset_id": "8b8b8c39c2bbe9a4da518ccf76728108edb9cbd544c3b8717dad2bbafbbf9e06",
                "genesis_point": "9da69d2096225bb8ff8220ee1c05fa381e0654743bebb1c31f23c73d5894d9a5:1",
                "total_supply": "1000",
                "asset_name": "NoDecimals",
                "asset_type": "NORMAL",
                "genesis_height": 335,
                "genesis_timestamp": "1748354548",
                "anchor_point": "caaa428cf8ffba920fbff77812ed201fa5915862145b3bf5a071d0ef362ad9e2:0",
                "decimal_display": 0
            },
            "total_syncs": "0",
            "total_proofs": "1"
        },
    ]
}

My biggest concern with the approach I took here is the performance implications of looking up the decimal display at the rpcserver level, so this compute isn't cached along with the other queried data. This RPC is already pretty slow, and adding more to it may likely degrade performance further. I couldn't figure out how to obtain the decimal display in the QuerySyncStats function, which would include the results in the cache. Please let me know if there are any better ways of doing this.

[guggero]

Nice, LGTM 🎉

[coveralls]

Pull Request Test Coverage Report for Build 15277888381

Details

• 0 of 5 (0.0%) changed or added relevant lines in 1 file are covered.
• 33 unchanged lines in 6 files lost coverage.
• Overall coverage decreased (-0.05%) to 37.122%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
rpcserver.go	0	5	0.0%

Files with Coverage Reduction	New Missed Lines	%
commitment/tap.go	1	72.05%
internal/test/helpers.go	2	86.48%
tapchannel/aux_leaf_signer.go	2	43.08%
address/address.go	6	67.47%
tapdb/multiverse.go	6	53.03%
address/mock.go	16	88.24%

Totals
Change from base Build 15255103485:	-0.05%
Covered Lines:	26972
Relevant Lines:	72658

---

💛 - Coveralls