Fix completion suggesting --self for class-grouped commands

[shivamtiwari3]

Fixes google/python-fire issue #382: #382

What happened
When using a class as the Fire component (to group commands), Fire’s --completion output could include the implicit bound argument self as a CLI flag (--self). This is confusing and incorrect since users can never pass self explicitly.

Example symptom (from completion script output):

opts="--arg1 --self ${GLOBAL_OPTIONS}"
opts="--self ${GLOBAL_OPTIONS}"
Root cause
The completion generator builds option flags from the callable’s argspec:

Completions() → inspectutils.GetFullArgSpec(component) → _CompletionsFromArgs(spec.args + spec.kwonlyargs)
For unbound methods (functions retrieved from a class), spec.args includes self (or cls), because Python includes that parameter in the signature even though it is implicitly supplied at call time.
_CompletionsFromArgs was converting every arg name into a -- completion, which incorrectly produced --self.

Fix
In fire/completion.py, _CompletionsFromArgs now skips a leading self / cls argument when present. This ensures completion suggestions only contain user-supplied parameters.

This is a minimal, targeted change that affects only completion flag generation from argument lists.

Reproduction
A standalone repro script is included:

python3 repro_issue_382.py
It generates completion output for a small example class and asserts that --self is not present in the completion script.

Tests
python3 -m unittest fire.completion_test -q
Notes
This change is limited to completion generation. It does not affect Fire’s argument parsing or invocation behavior.
Existing test testMethodCompletions already asserts that --self should not appear; this change ensures the completion script output also respects that constraint in the class-grouping scenario.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.