Add fault header inequality matchers

[shashankv02]

💸 TL;DR

Port of https://github.snooguts.net/reddit-go/faultbp/pull/30

Adds inequality matching for fault selectors so operators can fault broad request sets while excluding known-safe dependencies without introducing a grouping syntax.

The matcher keys a, h, and m now accept != in addition to =. Multiple matcher segments in a single config are ANDed, so an exclusion list can be written as repeated address inequalities.

📜 Details

Syntax

<matchers>;<actions>

• Matcher keys: a=, a!=, h=, h!=, m=, m!=.
• A config still needs at least one a matcher to match a request.
• Multiple matchers in one config are ANDed.
• Action keys are unchanged: d, D, f, b, F.
• Multiple configs are still comma-separated and evaluated first-match-wins.

Examples

# Fault every outgoing request with 500 except critical-service, deciderpb.Decider,
# and foo.bar's Healthcheck method.
x-bp-fault: a!=critical-service;a!=deciderpb.Decider;a!=foo.bar;f=500,a=foo.bar;m!=Healthcheck;f=500

# Fault every method on foo.bar except Healthcheck.
x-bp-fault: a=foo.bar;m!=Healthcheck;f=500

🧪 Testing Steps / Validation

Added Unit tests

✅ Checks

• CI tests (if present) are passing
• Adheres to code style for repo
• Contributor License Agreement (CLA) completed if not a Reddit employee