feat: normalize the surface interface of Python SDK

[christianalfoni]

Normalize the Python SDK surface to flat keyword arguments

The Python SDK previously required users to import auto-generated request/body classes (CreateSandboxBody, CreateExecRequest, ExecStdin, StartOptions, CreateSandboxParams) and pass them as a single body or params argument. This branch flattens the public surface so calls read like idiomatic Python — no auto-generated types in user code, no StartOptions(...) wrappers — and folds in the new retry plumbing from main.

❌ Current behavior

from together_sandbox import StartOptions, CreateSandboxParams
from together_sandbox.api.models.create_sandbox_body import CreateSandboxBody
from together_sandbox.sandbox.models.create_exec_request import CreateExecRequest
from together_sandbox.sandbox.models.update_exec_request import UpdateExecRequest
from together_sandbox.sandbox.models.exec_stdin import ExecStdin

# Sandbox lifecycle — wrap everything in body objects
sandbox = await sdk.sandboxes.create(CreateSandboxParams(
    millicpu=1000, memory_bytes=2_000_000_000, disk_bytes=10_000_000_000,
    snapshot_alias="my-app@v1",
))
sb = await sdk.sandboxes.start(sandbox.id, start_options=StartOptions(version_number=3))

# Exec — wrap, then call generic update() with a status enum
exec_ = await sb.execs.create(CreateExecRequest(
    command="npm", args=["start"], cwd="/workspace",
))
await sb.execs.update(exec_.id, UpdateExecRequest(status="running"))
await sb.execs.send_stdin(exec_.id, ExecStdin(input="ls\n"))
# (no resize method)

✅ New behavior

# Sandbox lifecycle — flat kwargs, no body imports
sandbox = await sdk.sandboxes.create(
    millicpu=1000, memory_bytes=2_000_000_000, disk_bytes=10_000_000_000,
    snapshot_alias="my-app@v1",
)
sb = await sdk.sandboxes.start(sandbox.id, version_number=3)

# Exec — flat kwargs, intent-named verbs
exec_ = await sb.execs.create(
    "npm", ["start"], cwd="/workspace", env={"NODE_ENV": "production"},
)
await sb.execs.resume(exec_.id)              # was execs.update(..., status="running")
await sb.execs.send_stdin(exec_.id, "ls\n")  # raw str, no ExecStdin wrapper
await sb.execs.resize(exec_.id, cols=80, rows=24)  # new

🤔 Assumptions

• Users never directly construct CreateSandboxBody / CreateExecRequest / ExecStdin — they're internal wire types, not API ergonomics.
• The only valid update_exec status today is "running", so update() is best modeled as resume().
• The PTY wire format "{cols}x{rows}" for resize is what the agent expects (flagged in the docstring as not yet end-to-end verified).
• The retry config (RetryConfig / RetryContext) introduced on main should be re-exported from the package root alongside the other public types.

🧠 Decisions

• Normalized op-names to a dotted convention everywhere ("sandboxes.start", "sandboxes.wait", "sandboxes.create", "execs.resume", "execs.sendStdin", "execs.resize") so users filtering on RetryContext.operation see a consistent namespace.
• Deleted together_sandbox/_types.py (StartOptions, CreateSandboxParams) — the flat-kwargs signatures replace them entirely.
• Kept the auto-generated body classes available as imports for advanced users, but no longer reference them in the surface API or docs.

🔄 Discussions

• Mid-merge, the _call_api-based tests fail when mocks return bare model instances instead of Response[...] wrappers. Added the make_api_response / make_sandbox_response helpers to every patched mock and updated the error-path tests' regex matchers to the dotted op-name format.
• _sandboxes.py originally landed three camelCase op-names from main. Renamed to dotted form during the merge so retry hooks see the same convention across the package.

🧪 Testing

• Conflict resolution verified: git grep '<<<<<<< \|=======$\|>>>>>>> ' returns nothing across the workspace.
• Updated unit tests in together-sandbox-python/tests/test_facade.py cover: SandboxesNamespace.create body construction (required-only + all optional kwargs), Execs.create flat-kwargs and env dict wrapping, Execs.resume sending RUNNING, Execs.send_stdin and Execs.resize body shapes, plus error-path matchers for the new dotted op-names.
• pytest tests/ -v passes locally.

📁 References

• together-sandbox-python/together_sandbox/init.py
• together-sandbox-python/together_sandbox/_sandbox.py
• together-sandbox-python/together_sandbox/_sandboxes.py
• together-sandbox-python/tests/test_facade.py
• docs/python-sdk.md

[christianalfoni]

Note! This file is deleted in the E2E tests PR, so can just ignore it