Broadcasting BlockRange by integer types doesn't perform proper conversions

Broadcasting BlockRange by integer types doesn't perform proper conversions, for example:

julia> Int32.(Block(1):Block(3))
1:3

julia> eltype(Int32.(Block(1):Block(3)))
Int

This is caused by this broadcasting definition:
https://github.com/JuliaArrays/BlockArrays.jl/blob/cd73466e5e1783cf6176a0091a5838c1f2a49798/src/blockindices.jl#L537
which was a sloppy definition I accidentally introduced in https://github.com/JuliaArrays/BlockArrays.jl/pull/405 when generalizing block index types beyond Int. It could be fixed by changing that definition too:

broadcasted(::DefaultArrayStyle{1}, ::Type{T}, block_range::BlockRange{1}) where {T <: Integer} = convert(AbstractUnitRange{T}, first(block_range.indices))

Ideally we would use:

broadcasted(::DefaultArrayStyle{1}, ::Type{T}, block_range::BlockRange{1}) where {T <: Integer} = T.(first(block_range.indices))

but broadcasting unit ranges with integer types doesn't preserve unit ranges in Base right now:

julia> Int32.(1:3)
3-element Vector{Int32}:
 1
 2
 3

Version info:

julia> versioninfo()
Julia Version 1.12.4
Commit 01a2eadb047 (2026-01-06 16:56 UTC)
Build Info:
  Official https://julialang.org release
Platform Info:
  OS: macOS (arm64-apple-darwin24.0.0)
  CPU: 10 × Apple M1 Max
  WORD_SIZE: 64
  LLVM: libLLVM-18.1.7 (ORCJIT, apple-m1)
  GC: Built with stock GC
Threads: 1 default, 1 interactive, 1 GC (on 8 virtual cores)
Environment:
  JULIA_EDITOR = code

julia> pkgversion(BlockArrays)
v"1.9.3"

Start in src/blockindices.jl at the broadcasted definition linked in the issue, and reproduce the Int32.(Block(1):Block(3)) examples in Julia. Check that the chosen conversion preserves the expected integer element type and range behavior, then verify both the displayed result and eltype against the issue’s examples.