Add inherit_env and login_shell submit options

[krokicki]

Summary

• By default, jobs inherit the submitting process's full environment (Popen merges os.environ locally; bsub copies the caller's environment on LSF), which leaks whatever the submitter happened to have set (e.g. PIXI_PROJECT_MANIFEST, worker-internal vars). Two new submit() kwargs let callers construct the job's environment instead of inheriting it:
  • inherit_env=False — local jobs get a minimal baseline (identity vars + fixed PATH) plus any explicit env; LSF submits with -env none, and explicit env vars move into the script as exports since bsub will no longer copy them.
  • login_shell=True — run under a login shell (bash -l locally, bsub -L /bin/bash on LSF) so the target user's own profile builds PATH/modules/conda, as an SSH session would.
• Defaults (inherit_env=True, login_shell=False) preserve existing behavior — this is purely additive.

Stacked on #3 (fix-cross-user-polling) since that's what it was branched from; the diff here is only the new commit.

Why

fileglancer's cluster-job launcher needs to stop leaking its own process environment into every submitted job. This library needs the explicit inherit_env/login_shell controls before fileglancer's PR can be un-blocked and released against.

Test plan

• pixi run test — 162 passed (new coverage in tests/test_local.py and tests/test_lsf.py)
• Release a new version to PyPI once merged, so downstream (fileglancer) can bump its pin

@StephanPreibisch @JaneliaSciComp/fileglancer