docs: document Algorithm and Opt

[ChrisRackauckas-Claude]

Adds source-owned API docstrings for the exported Algorithm and Opt bindings. The Algorithm attachment follows the conditional enum declaration because the enum is selected by the linked NLopt version; Opt documents its construction, ownership/lifetime behavior, fields, errors, and usage.

Adds a focused regression test that verifies both public bindings are present in NLopt documentation metadata.

Please ignore until reviewed by @ChrisRackauckas.

Verification

• julia --startup-file=no --project=. -e 'using NLopt; docs = Base.Docs.meta(NLopt); @assert haskey(docs, Base.Docs.Binding(NLopt, :Algorithm)); @assert haskey(docs, Base.Docs.Binding(NLopt, :Opt)); println("registered public docstrings")'\n - registered public docstrings\n- julia --startup-file=no --project=. -e 'using Pkg; Pkg.test()'\n - test_runtests | 2278 2278 17m17.1s\n - Testing NLopt tests passed\n- julia --startup-file=no --project=. -e 'using JuliaFormatter; format("src"); format("test")'\n- git diff --check\n- git diff -- src/NLopt.jl test/C_API.jl | typos -\n\nNo documentation build was run because this repository has no docs/ project.\n\n🤖 Generated with Claude Code\nhttps://chatgpt.com/codex/tasks/019f4028-d2ae-7a12-aff0-7d996bd9c791

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.75%. Comparing base (f84a501) to head (7b81927).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #279   +/-   ##
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  Coverage   99.75%   99.75%           
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  Files           2        2           
  Lines         805      805           
=======================================
  Hits          803      803           
  Misses          2        2           

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