Cannot append DictEncode columns to Stream

On Arrow v2.7.1 (and Julia v1.10.1):

```julia
julia> t = (; a = Arrow.DictEncode([:a]))
(a = [:a],)

julia> Arrow.write("x.stream.arrow", t, file = false)
"x.stream.arrow"

julia> Arrow.append("x.stream.arrow", t)
ERROR: ArgumentError: Table schema does not match existing arrow file schema
Stacktrace: [...]
```

The problem is that the `NamedTuple` has

```julia
julia> Tables.schema(t).types
(Arrow.DictEncodeType{Symbol},)
```

while the stream is identified as

```julia
julia> s = open("x.stream.arrow", "r+") do io
Arrow.stream_properties(io)
end;
julia> s[2].types
(Symbol,)
```

and there doesn't seem to be an easy workaround because `append` doesn't allow overriding the `arrow_schema` without effectively duplicating the other append methods' code on the user side. Omitting the `Arrow.DictEncode` on subsequent segments doesn't work either:

```julia
julia> t2 = (; a = [:b])
(a = [:b],)

julia> Arrow.append("x.stream.arrow", t2)
"x.stream.arrow"

julia> d = Arrow.Table("x.stream.arrow")
Arrow.Table with 9 rows, 1 columns, and schema:
:a Symbol

julia> d.a
9-element SentinelArrays.ChainedVector{Symbol, Arrow.DictEncoded{Symbol, Int8, Arrow.List{Symbol, Int32, Vector{UInt8}}}}:
Error showing value of type SentinelArrays.ChainedVector{Symbol, Arrow.DictEncoded{Symbol, Int8, Arrow.List{Symbol, Int32, Vector{UInt8}}}}:
ERROR: ArgumentError: Symbol name may not contain \0
```

I am unsure whether changing [`is_equivalent_schema`](https://github.com/apache/arrow-julia/blob/ac199b0e377502ea0f1fa5ced7fda897a01b82a9/src/append.jl#L280) would fix the issue because I don't understand if the downstream code ([`toarrowtable`](https://github.com/apache/arrow-julia/blob/ac199b0e377502ea0f1fa5ced7fda897a01b82a9/src/write.jl#L508)?) can handle unequal schemas like this.

Please advise.

Reproduce the failure with the Arrow.DictEncode examples, then inspect src/append.jl at is_equivalent_schema and src/write.jl at toarrowtable. Determine whether append can safely handle the DictEncodeType versus Symbol schema difference, including the later read failure. Done means the stream can be appended and read without the reported schema or NUL-symbol errors.

Written by the indexing model from the issue text.