feat: add filtering options to list-sources

[patrick204nqh]

Summary

• Add --collector flag to filter by collector name before fetching sources (avoids unnecessary API calls)
• Add -n/--name flag to filter sources by name
• Add --category flag to filter sources by category
• Add -l/--limit flag to cap total sources returned
• All filters are case-insensitive substring matches

Details

The key optimization is pre-filtering collectors by name before the parallel source fetch. In environments with 200+ collectors, specifying --collector "my-service" might narrow down to 3-5 collectors, eliminating ~98% of API calls and avoiding rate-limit errors.

Source-level filters (--name, --category) are applied as post-filters after fetching. Collectors with no matching sources after filtering are excluded from output. --limit is applied last, capping total sources across all collectors.

Files changed:

• lib/sumologic/cli.rb — Thor option declarations and updated help text
• lib/sumologic/cli/commands/list_sources_command.rb — Pass filter options to client
• lib/sumologic/metadata/source.rb — Collector pre-filter, source post-filter, limit logic
• lib/sumologic/client.rb — Updated list_all_sources facade signature
• spec/sumologic/metadata/source_spec.rb — New: 11 tests for filtering/limiting
• spec/sumologic/cli/commands/commands_spec.rb — Updated command tests

Test plan

• 11 new metadata tests: collector filter, source name/category filter, combined filters, limit, filter+limit, empty result exclusion
• Updated command spec verifies filter option passthrough
• Full suite: 169/169 passing

Closes #12