Fix anonymous method serialization for Julia v1.10

[topolarity]

This appears to be enough to resolve #124:

julia> versioninfo()
Julia Version 1.10.0
Commit 3120989f39b (2023-12-25 18:01 UTC)
...
julia> using BSON

julia> f = x -> x+1
       #1 (generic function with 1 method)
#1 (generic function with 1 method)

julia> f2 = BSON.roundtrip(f) # ok 
#1 (generic function with 1 method)

fwiw, I have not done a careful review of the serialization logic - this is just an effort to patch the conspicuous regressions