feat: add support for the --all to proxy remove

[eureka928]

Summary

Refactor of #791, addressing reviewer feedback from @thewhaleking.

This PR adds the --all flag to btcli proxy remove so users can remove all proxies in a single operation. The two review comments on #791 have been addressed:

1. Error on conflicting args instead of warning (comment): Providing --delegate together with --all now returns an error instead of silently ignoring the delegate.
2. Combine into single function with a flag (comment): The separate remove_proxies() function has been merged into the existing remove_proxy() function using a remove_all: bool = False parameter, reducing code duplication.

Type of change

• New feature (non-breaking)
• Refactor (addresses code review feedback)

What's changed

File	Change
`bittensor_cli/cli.py`	Added `--all` flag to `proxy_remove` command; validation rejects conflicting `--delegate` + `--all`; routes `remove_all` flag to the unified function
`bittensor_cli/src/commands/proxy.py`	Combined `remove_proxies()` into `remove_proxy()` with `remove_all` flag; branches prompt, call composition, and extrinsic based on the flag
`tests/e2e_tests/test_proxy.py`	E2E tests: remove all proxies, validation errors, single proxy removal
`tests/unit_tests/test_cli.py`	Unit tests: missing args error, conflicting args error, `--all` flag routing, single delegate routing

CLI validation flow

1. Neither `--delegate` nor `--all` provided → error
2. Both `--delegate` and `--all` provided → error
3. `--all` only → calls `remove_proxy(..., remove_all=True)`
4. `--delegate` only → calls `remove_proxy(..., remove_all=False)`

Usage

```bash

Remove a single proxy

btcli proxy remove --delegate 5GDel... --proxy-type Transfer --delay 0

Remove all proxies (requires typing "REMOVE" to confirm)

btcli proxy remove --all

Remove all proxies without prompt

btcli proxy remove --all --no-prompt
```

Testing

Unit tests

```
$ pytest tests/unit_tests/test_cli.py -v -k proxy
tests/unit_tests/test_cli.py::test_proxy_remove_requires_delegate_or_all PASSED
tests/unit_tests/test_cli.py::test_proxy_remove_requires_delegate_or_all_json PASSED
tests/unit_tests/test_cli.py::test_proxy_remove_with_all_and_delegate_errors PASSED
tests/unit_tests/test_cli.py::test_proxy_remove_with_all_flag PASSED
tests/unit_tests/test_cli.py::test_proxy_remove_with_delegate_calls_remove_proxy PASSED
```

Lint

```
$ ruff format --check bittensor_cli tests
All checks passed!
```

Checklist

• Code follows project style (ruff)
• Self-reviewed changes
• Unit tests added and passing
• E2E tests added
• No new warnings introduced
• Reviewer feedback from Add support for the --all to proxy remove #791 addressed

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[eureka928]

Hi @thewhaleking would you review my PR?
Thank you