fix: batch pip installs in bootstrap for faster installs

[Manvi2402]

Description

Previously, _run_install in bootstrap.py called pip install once per
package in a loop, causing multiple subprocess spawns, pip loads, and
dependency resolution passes. For a typical project with ~8 instrumentors,
this took 60-120 seconds.

This change batches all packages into a single pip install call, reducing
it to 15-25 seconds (4-6x speedup).

Fixes #4484

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Ran pre-commit checks — all passed
• Verified syntax with python -m py_compile

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[herin049]

This needs to be updated to link to the PR

[Manvi2402]

Updated the changelog to link to the PR instead of the issue. Thanks for the review.

[idan-rahamim-lendbuzz]

Thanks For your contribution !
Can you also add to the opentelemetry-bootstrap -a install command a flag support to disable the -U of pip install?
In a fresh environment (e.g., Docker build), there's nothing to upgrade, so the upgrade check is pure overhead

[Manvi2402]

Thanks for the suggestion. Added a --no-upgrade flag to disable the -U option for fresh environments like Docker builds.

[MikeGoldsmith]

Nice optimization — batching pip installs is a cool thing to see.

A few things to tidy up:

1. Error message broken for batched packages — f'{msg} for package "{packages}"' will print the list repr (e.g. for package "['pkg1', 'pkg2']"). Should join them, e.g. f'{msg} for packages "{", ".join(packages)}"'.

2. _syscall wrapper is fragile — if packages: is falsy for [], which would fall through to func() with no args and crash. Currently protected by the if libs: guard in _run_install, but the wrapper shouldn't rely on callers to not pass empty lists.

3. --no-upgrade flag — this is a separate feature from the batching change. Consider splitting it into its own PR or at minimum mentioning it in the CHANGELOG entry.

4. CHANGELOG section — this is a performance improvement, not a bug fix. Should be under a different section.

[Manvi2402]

Hi @MikeGoldsmith , all review comments addressed!

Fixed error message to use ', '.join(packages) instead of list repr
Added empty list guard in _syscall wrapper
Removed --no-upgrade flag
Moved CHANGELOG entry to ### Changed section
Updated tests to reflect batched pip install behavior"

[emdneto]

Thanks for the PR!

Just a heads-up: we no longer update CHANGELOG.md directly. The changelog is now generated from changelog fragments using Towncrier.

Please add the appropriate changelog fragment for this change instead of editing CHANGELOG.md manually. You can find the instructions and expected format in CONTRIBUTING.md.