Loosen type restriction on Ryu.writeshortest (#57172)

`Ryu.writeshortest` is documented to have a method that "allows passing
in a byte buffer", just like `Ryu.writefixed` and `Ryu.writeexp`, but
unlike those functions `writeshortest` is type constrained to
`::Vector{UInt8}`. This PR loosens that to `::AbstractVector{UInt8}`, to
allow the "byte buffer" to e.g. be a `Memory` rather than a `Vector`.

I've added tests and updated the docstrings for all three functions to
ensure that they're not just restricted to `Vector{UInt8}`.

This change was prompted by our private codebase hitting `MethodError:
no method matching writeshortest(::Memory{UInt8}, ::Int64, ::Float64,
...)` when trying it out with Julia v1.12.0-DEV.
 
(cc @quinnj -- i think you added this method originally, but i couldn't
see any reason why e.g. Memory shouldn't be allowed now we have it)

base/ryu/Ryu.jl

@@ -19,7 +19,7 @@ neededdigits(::Type{Float16}) = 9 + 5 + 9
 
 """
     Ryu.writeshortest(x, plus=false, space=false, hash=true, precision=-1, expchar=UInt8('e'), padexp=false, decchar=UInt8('.'), typed=false, compact=false)
-    Ryu.writeshortest(buf::Vector{UInt8}, pos::Int, x, args...)
+    Ryu.writeshortest(buf::AbstractVector{UInt8}, pos::Int, x, args...)
 
 Convert a float value `x` into its "shortest" decimal string, which can be parsed back to the same value.
 This function allows achieving the `%g` printf format.
@@ -53,7 +53,7 @@ end
 
 """
     Ryu.writefixed(x, precision, plus=false, space=false, hash=false, decchar=UInt8('.'), trimtrailingzeros=false)
-    Ryu.writefixed(buf::Vector{UInt8}, pos::Int, x, args...)
+    Ryu.writefixed(buf::AbstractVector{UInt8}, pos::Int, x, args...)
 
 Convert a float value `x` into a "fixed" size decimal string of the provided precision.
 This function allows achieving the `%f` printf format.
@@ -81,7 +81,7 @@ end
 
 """
     Ryu.writeexp(x, precision, plus=false, space=false, hash=false, expchar=UInt8('e'), decchar=UInt8('.'), trimtrailingzeros=false)
-    Ryu.writeexp(buf::Vector{UInt8}, pos::Int, x, args...)
+    Ryu.writeexp(buf::AbstractVector{UInt8}, pos::Int, x, args...)
 
 Convert a float value `x` into a scientific notation decimal string.
 This function allows achieving the `%e` printf format.

base/ryu/shortest.jl

@@ -224,7 +224,7 @@ integer. If a `maxsignif` argument is provided, then `b < maxsignif`.
     return b, e10
 end
 
-function writeshortest(buf::Vector{UInt8}, pos, x::T,
+function writeshortest(buf::AbstractVector{UInt8}, pos, x::T,
                        plus=false, space=false, hash=true,
                        precision=-1, expchar=UInt8('e'), padexp=false, decchar=UInt8('.'),
                        typed=false, compact=false) where {T}

test/ryu.jl

@@ -370,6 +370,23 @@ end
 
 end # Float16
 
+@testset "writeshortest(::AbstractVector, pos, ...)" begin
+    @testset for Vec in (Vector{UInt8}, Memory{UInt8})
+        buf = Vec(undef, 4)
+        @test Ryu.writeshortest(buf, 1, -0.0) == 5
+        @test String(buf) == "-0.0"
+
+        buf = Vec(undef, 100)
+        xx = 4.7223665f21
+        expected = "4.7223665e21"
+        start_pos = 42
+        nwritten = length(expected)
+        end_pos = start_pos + nwritten
+        @test Ryu.writeshortest(buf, start_pos, xx) == end_pos
+        @test String(buf[start_pos:end_pos-1]) == expected
+    end
+end
+
 @testset "Ryu.writefixed" begin
     @testset "Basic" begin
         @test Ryu.writefixed(todouble(false, 1234, 99999), 0) ==
@@ -563,6 +580,23 @@ end # Float16
     @test Ryu.writefixed(-100.0+eps(-100.0), 0, false, false, true, UInt8('.'), false) == "-100."
     @test Ryu.writefixed(100.0-eps(100.0), 1, false, false, true, UInt8('.'), false) == "100.0"
     @test Ryu.writefixed(-100.0+eps(-100.0), 1, false, false, true, UInt8('.'), false) == "-100.0"
+
+    @testset "writefixed(::AbstractVector, pos, ...)" begin
+        @testset for Vec in (Vector{UInt8}, Memory{UInt8})
+            buf = Vec(undef, 6)
+            @test Ryu.writefixed(buf, 1, 0.0, 4) == 7
+            @test String(buf) == "0.0000"
+
+            buf = Vec(undef, 100)
+            xx = 1729.142857142857
+            prec = 8
+            start_pos = 42
+            nwritten = 4 + 1 + prec
+            end_pos = start_pos + nwritten
+            @test Ryu.writefixed(buf, start_pos, xx, prec) == end_pos
+            @test String(buf[start_pos:end_pos-1]) == "1729.14285714"
+        end
+    end
 end # fixed
 
 @testset "Ryu.writeexp" begin
@@ -761,6 +795,23 @@ end
     @test Ryu.writeexp(2.0, 1, false, false, false, UInt8('e'), UInt8('.'), true) == "2e+00"
 end
 
+@testset "writeexp(::AbstractVector, pos, ...)" begin
+    @testset for Vec in (Vector{UInt8}, Memory{UInt8})
+        buf = Vec(undef, 10)
+        @test Ryu.writeexp(buf, 1, 0.0, 4) == 11
+        @test String(buf) == "0.0000e+00"
+
+        buf = Vec(undef, 100)
+        xx = 1729.142857142857
+        prec = 8
+        start_pos = 42
+        nwritten = 1 + 1 + prec + 4
+        end_pos = start_pos + nwritten
+        @test Ryu.writeexp(buf, start_pos, xx, prec) == end_pos
+        @test String(buf[start_pos:end_pos-1]) == "1.72914286e+03"
+    end
+end
+
 end # exp
 
 @testset "compact" begin