feat(python-sdk): use pyqwest native HTTP/2 connection balancing

[devin-ai-integration]

Summary

curioswitch/pyqwest#246 adds client-side load balancing to pyqwest's pool: it spreads an origin's HTTP/2 streams over connections by free stream capacity (from the server's SETTINGS_MAX_CONCURRENT_STREAMS), dials another connection only once every existing one is full, and caps connections per resolved address via max_connections_per_address. That is what our Python-side ConnectionBalancer / BalancingTransport did by fanning out over multiple pyqwest transports, so this PR drops them and uses one native transport.

# before: ConnectionRetryTransport(BalancingTransport(ConnectionBalancer(build)))
# after
ConnectionRetryTransport(
    SyncHTTPTransport(..., max_connections_per_address=max_connections),  # HTTPTransport for async
    max_retries=connection_retries,
)

• E2B_MAX_CONNECTIONS (default 200) now maps to max_connections_per_address. Past the cap, a request waits for a stream on an existing connection (previously: piled onto the least-loaded one, same effect).
• E2B_STREAMS_PER_CONNECTION is removed — the per-connection limit now comes from the server (envd edge advertises 100).
• Removed ConnectionBalancer, PooledConnection, request_origin, BalancingTransport, _TrackedContent; response-lifetime slot accounting is now handled by pyqwest holding the hyper-util connection lease in response extensions until the body completes/closes.
• test_envd_stream_capacity.py rewritten to assert the native pool's behavior against the local HTTP/2 frame server (waves of 80 streams at a 100-stream limit → 1, 2, 3 connections, freed streams reused; at a cap of 2 connections × 10 streams the 21st request waits until a stream closes), sync and async. Balancer unit tests removed.

Unreleased pyqwest — do not release until fixed

pyqwest with #246 is not on PyPI yet, so packages/python-sdk/pyproject.toml pins it via a [tool.uv.sources] git source at the merge commit c4aae51 (version 0.11.0 there) and the floor is bumped to pyqwest>=0.11.0,<0.12. The code-interpreter-python and desktop-python lockfiles are relocked because they pull e2b from the workspace path and inherit that source. tool.uv.sources is not included in published metadata, so before merging/releasing: drop the source block, set the floor to the actual pyqwest release, and uv lock all three packages. Until then, uv sync builds pyqwest from source (needs a Rust toolchain; ~1.5 min). pyqwest#246 also builds against [patch.crates-io] forks of h2/hyper/hyper-util — worth confirming those land upstream (or that pyqwest ships wheels built from them) before relying on it.

Link to Devin session: https://app.devin.ai/sessions/81af1a093fda4f22a89e3c1e4d78047c
Open in Devin Desktop: https://app.devin.ai/desktop/session/81af1a093fda4f22a89e3c1e4d78047c?variant=devin
Requested by: @mishushakov

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring

[changeset-bot]

🦋 Changeset detected

Latest commit: a5c3bc1

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@e2b/python-sdk	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[devin-ai-integration]

Checked the changed code for parity (T-1–T-2), API shape and exports (T-3, T-54), streaming and timeouts (T-26–T-31, T-45–T-48), configuration (T-49–T-53), compatibility (T-65–T-68), and documentation (T-69–T-74): 0 TASTE violations found.

[github-actions]

Package Artifacts

Built from 57199b9. Download artifacts from this workflow run.

JS SDK (e2b@2.52.1-devin-1790937617-pyqwest-native-balancing.0):

npm install ./e2b-2.52.1-devin-1790937617-pyqwest-native-balancing.0.tgz

CLI (@e2b/cli@2.21.1-devin-1790937617-pyqwest-native-balancing.0):

npm install ./e2b-cli-2.21.1-devin-1790937617-pyqwest-native-balancing.0.tgz

Code Interpreter JS SDK (@e2b/code-interpreter@2.8.1-devin-1790937617-pyqwest-native-balancing.0):

npm install ./e2b-code-interpreter-2.8.1-devin-1790937617-pyqwest-native-balancing.0.tgz

Desktop JS SDK (@e2b/desktop@2.4.1-devin-1790937617-pyqwest-native-balancing.0):

npm install ./e2b-desktop-2.4.1-devin-1790937617-pyqwest-native-balancing.0.tgz

Python SDK (e2b==2.52.0+devin.1790937617.pyqwest.native.balancing):

pip install ./e2b-2.52.0+devin.1790937617.pyqwest.native.balancing-py3-none-any.whl

Code Interpreter Python SDK (e2b-code-interpreter==2.10.1+devin.1790937617.pyqwest.native.balancing):

pip install ./e2b_code_interpreter-2.10.1+devin.1790937617.pyqwest.native.balancing-py3-none-any.whl

Desktop Python SDK (e2b-desktop==2.6.0+devin.1790937617.pyqwest.native.balancing):

pip install ./e2b_desktop-2.6.0+devin.1790937617.pyqwest.native.balancing-py3-none-any.whl