Introduce compact keys for JSON metadata fields to reduce size of JSON metadata object

[kuan121]

High Level Changes

1. Introduce compact keys for JSON metadata fields to reduce size of JSON metadata object
2. Remove unnecessary URL scheme, i.e., HTTPS://

Why

This PR is meant to address WietseWind's comment in this discussion about reducing the size of JSON metadata object. With the proposed change, we can achieve a ~27.6% size reduction (from ~626 bytes to ~453 bytes) for the JSON Metadata example provided in XLS-89 Multi-Purpose Token Metadata Schema.

Before

JSON Metadata example (626 bytes)

{
  "ticker": "TBILL",
  "name": "T-Bill Yield Token",
  "desc": "A yield-bearing stablecoin backed by short-term U.S. Treasuries and money market instruments.",
  "icon": "https://example.org/tbill-icon.png",
  "asset_class": "rwa",
  "asset_subclass": "treasury",
  "issuer_name": "Example Yield Co.",
  "urls": [
    {
      "url": "https://exampleyield.co/tbill",
      "type": "website",
      "title": "Product Page"
    },
    {
      "url": "https://exampleyield.co/docs",
      "type": "docs",
      "title": "Yield Token Docs"
    }
  ],
  "additional_info": {
    "interest_rate": "5.00%",
    "interest_type": "variable",
    "yield_source": "U.S. Treasury Bills",
    "maturity_date": "2045-06-30",
    "cusip": "912796RX0"
  }
}

After

JSON Metadata example (453 bytes)

{
  "t": "TBILL",
  "n": "T-Bill Yield Token",
  "d": "A yield-bearing stablecoin backed by short-term U.S. Treasuries and money market instruments.",
  "i": "example.org/tbill-icon.png",
  "ac": "rwa",
  "as": "treasury",
  "in": "Example Yield Co.",
  "us": [
    {
      "u": "exampleyield.co/tbill",
      "c": "website",
      "t": "Product Page"
    },
    {
      "u": "exampleyield.co/docs",
      "c": "docs",
      "t": "Yield Token Docs"
    }
  ],
  "ai": {
    "interest_rate": "5.00%",
    "interest_type": "variable",
    "yield_source": "U.S. Treasury Bills",
    "maturity_date": "2045-06-30",
    "cusip": "912796RX0"
  }
}

[julian78780]

Hey @WietseWind - this PR reflects the key proposals from our earlier discussions, and we’re aligned with the direction.

We propose to use the short-key format only, primarily for simplicity and to be sensible about on-ledger storage, given that all of this data is immutable once written. We also agree that we should avoid maintaining multiple standards over time, so let’s aim to settle on this one.

We’ll keep this PR open for two weeks for comments, and plan to merge afterward unless there are major objections.

Regarding encoding, we’d prefer to keep it as JSON. As you mentioned, it’s the simplest and most approachable option for the average developer.

For context, we’re also working on the XRPL Meta implementation, which will follow this short-key structure.

[WietseWind]

Wonderful, thanks. Agree on all fronts/

[Patel-Raj11]

LGTM!