refactor: Track updates, CategoryName

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@nordfjord

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(comment at time pf first commit)

maybe sid.Gen should be called streamId and kept private in the CategoryId impl?

then sid can be called catId or cid ?

as for sid.Category, maybe that means going back to it being a top level Literal? But it was actually good that the default was that people cant just randomly refer to Aggregate.Category from anywhere across the galaxy

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Tried to apply here but it does not make things better

However in a closed source codebase where things are symmetric (i.e. all SNs get roundtripped in tests or reactors), this helper works well

type internal CategoryId<'ids>(name, gen: 'ids -> FsCodec.StreamId, dec: FsCodec.StreamId -> 'ids) =
    member _.StreamName = gen >> FsCodec.StreamName.create name
    member _.DecodeId = dec
    member _.TryDecode = FsCodec.StreamName.tryFind name >> ValueOption.map dec

it also forces instances to be internal, e.g.

let [<Literal>] private CategoryName = "invitationprocess"
let private catId = CategoryId(CategoryName, streamId, FsCodec.StreamId.dec2 TenantId.parse InvitationId.parse)

which is consumed by tests and reactions via:

module Reactions =

    let [<return: Struct>] (|For|_|) = catId.TryDecode

    let dec = Streams.Codec.dec<Events.Event>
    let config = catId.StreamName, dec
    let [<return: Struct>] (|Decode|_|) = function
        | struct (For id, _) & Streams.Decode dec events -> ValueSome struct (id, events)
        | _ -> ValueNone
    let deletionNamePrefix tenantIdStr = $"%s{CategoryName}-%s{tenantIdStr}"

So maybe module Stream goes away in the guidance to be replaced with that canonical helper?

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related jet/FsCodec#103

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@nordfjord I ended up putting CategoryId into the mix in e0ed634 for any place where there's a .dec being used, which works well IME...
Now I need to update the docs

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(thought this was merging to master 🤦 - ended up cherry-picking it to master in 482203a)