chore: ignore b2's output directories

[jll63]

(Written by Claude Code, on behalf of @jll63.)

.gitignore covers build/, where CMake puts its tree, but not bin/, where b2 puts its
own. b2 makes one per project that has targets, so after a b2 test run the working tree
carries untracked object trees in five places:

bin/
test/bin/
test/dynamic_loading/bin/
test/implicit_shared_libraries/custom_registry/bin/
test/implicit_shared_libraries/default_registry/bin/

Untracked but addable is the awkward part: git add test or git add -A sweeps them in,
and one such commit runs to tens of thousands of lines of .o files. Nothing warns, because
nothing is wrong until it is committed. I managed exactly that twice while preparing #107 —
400 files and ~63,000 insertions each time — caught both from the diffstat and rebuilt the
commits, but the trap is worth closing rather than remembering.

doc/node_modules, the equivalent for the Antora build, is already covered by
doc/.gitignore.

Verification

• No tracked path in the repository contains a bin/ component (git ls-files | grep -E '(^|/)bin/' is empty), so the pattern hides nothing that is meant to be versioned.
• Checked both ways in a worktree that had just run b2 test: with the pattern,
  git status --porcelain reports 0 untracked entries; without it, 5.

🤖 Generated with Claude Code

https://claude.ai/code/session_01JQa4fuiwcfsheZYTCyfPPr

[cppalliance-bot]

An automated preview of the documentation is available at https://108.openmethod.prtest3.cppalliance.org/libs/openmethod/doc/html/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-09-12 16:17:06 UTC

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.52%. Comparing base (5ec487c) to head (89e753e).
⚠️ Report is 10 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #108      +/-   ##
===========================================
+ Coverage    93.46%   93.52%   +0.05%     
===========================================
  Files           22       22              
  Lines         1653     1683      +30     
  Branches       500      508       +8     
===========================================
+ Hits          1545     1574      +29     
  Misses          64       64              
- Partials        44       45       +1     

see 3 files with indirect coverage changes

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