fix map!(f,dest::ChainedVector,src::AbstractVector)

[laborg]

Fixes #115

With this PR the src is iterated instead of the probably longer destination.

Performance is better on this PR:

a,b=ChainedVector([rand(Int,5) for _ in 1:20000]),[1:100000...] # many chunks
@btime map!(i->-i,a,b)
# main: 188us
# pr: 153us

a,b=ChainedVector([[1:100000...]]),[1:100000...] # one chunk
@btime map!(i->-i,a,b)
# main: 171us
# pr: 73.8us

[quinnj]

[Reviewed by AI] Reviewed d179757d1480b996c56019e435be736058d0f5ed. No actionable findings in the changed overloads. The full suite passed locally on Julia 1.13/macOS arm64. Focused Base-vector checks cover empty and shorter sources, unchanged destination tails, chunk boundaries, and overlapping views. The short-source example fails on the base and passes here.