Update the ToString format of the BaseUnits/Dimensions

[lipchev]

• BaseUnits: no longer using the AbbeviationsCache, the new format is L=Meter, M=Kilogram, T=Second
• BaseDimensions: the exponent moved inside the dimension-brackets: [Length][Time^-1]
• BaseDimensions: minor performance improvements

As mentioned in #1452, the main motivation here is the removal of the potential side effects of accessing/loading the unit abbreviations (e.g. during the QuantityInfo construction)

[lipchev]

@angularsen Happy new year, here's an easy one which we've talked about in #1452

I wasn't 100% sure back then (and I never actually meant for it to be optimal), but I did a quick benchmark and the string.Join variant is just as fast (on net8.0) as the the StringBuilder with AppendFormat (but using much less allocations). The only variant in which the StringBuilder was slightly faster (but still more allocations) was this one (AI generated, haven't actually verified the output):

public string ToStringWithAppend()
{
    if (Equals(Undefined))
    {
        return "Undefined";
    }
    var sb = new StringBuilder();
    if (Length is not null)
    {
        sb.Append("[Length]: ").Append(Length).Append(", ");
    }
    if (Mass is not null)
    {
        sb.Append("[Mass]: ").Append(Mass).Append(", ");
    }
    if (Time is not null)
    {
        sb.Append("[Time]: ").Append(Time).Append(", ");
    }
    if (Current is not null)
    {
        sb.Append("[Current]: ").Append(Current).Append(", ");
    }
    if (Temperature is not null)
    {
        sb.Append("[Temperature]: ").Append(Temperature).Append(", ");
    }
    if (Amount is not null)
    {
        sb.Append("[Amount]: ").Append(Amount).Append(", ");
    }
    if (LuminousIntensity is not null)
    {
        sb.Append("[LuminousIntensity]: ").Append(LuminousIntensity).Append(", ");
    }
    if (sb.Length > 2)
    {
        sb.Length -= 2; // Remove the trailing ", "
    }
    return sb.ToString();
}

[angularsen]

Looks good to me, a couple of suggestions

[angularsen]

@angularsen Happy new year, here's an easy one which we've talked about in #1452

I meant to answer and forgot, happy new year @lipchev 🎉

I'm very glad you are around to learn from, and discuss and share ideas with, I really appreciate it ❤️
Also your energy and brilliance is exactly what this project needs to move things forward, I do not have as much time to spend on it as I would like to 🙇