perf: replace cidranger with bart for significant performance improvements (#675)

* feat: replace cidranger with bart improving performance by 3-20x

Signed-off-by: Jason Cameron <git@jasoncameron.dev>

* perf: replace cidranger with bart for IP range checking

- Replace cidranger.Ranger with bart.Lite in RemoteAddrChecker
- Use netip.ParsePrefix instead of net.ParseCIDR for modern IP handling
- Improve performance: 3-20x faster lookups with zero heap allocations
- Update imports to use github.com/gaissmai/bart and net/netip
- Remove cidranger dependency from go.mod

Benchmark results:
- IPv4 lookups: 4x faster (15.58ns vs 63.25ns, 0 vs 2 allocs)
- IPv6 lookups: 3x faster (26.51ns vs 76.96ns, 0 vs 2 allocs)
- Insertions: 20x faster (976ns vs 19,191ns)
- Large tables: 14x faster (5.2ns vs 74.85ns)

* docs: clarify CHANGELOG to not give false impressions

Signed-off-by: Jason Cameron <git@jasoncameron.dev>

* perf: optimize string concatenation in RemoteAddrChecker hash generation

Replace fmt.Fprintln with strings.Join for 7x faster performance:
- Before: 935.1 ns/op, 784 B/op, 22 allocs/op
- After: 133.2 ns/op, 192 B/op, 1 alloc/op

The hash is used for JWT cookie validation and error code generation.
Comma separation provides the same deterministic uniqueness as newlines
but with significantly better performance during policy initialization.

* chore: remove accidentally commited string benchmark

Signed-off-by: Jason Cameron <git@jasoncameron.dev>

* style: apply Copilot suggestions

Signed-off-by: Jason Cameron <git@jasoncameron.dev>

* fix: reference the right var name

i cannot write a merge commit

Signed-off-by: Jason Cameron <git@jasoncameron.dev>

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Signed-off-by: Jason Cameron <git@jasoncameron.dev>

.github/actions/spelling/allow.txt

@@ -2,4 +2,4 @@ github
 https
 ssh
 ubuntu
-workarounds
+workarounds

.github/actions/spelling/excludes.txt

@@ -86,4 +86,4 @@
 ^docs/manifest/.*$
 ^docs/static/\.nojekyll$
 ignore$
-robots.txt
+robots.txt

.github/actions/spelling/patterns.txt

@@ -131,4 +131,4 @@ go install(?:\s+[a-z]+\.[-@\w/.]+)+
 
 # hit-count: 1 file-count: 1
 # microsoft
-\b(?:https?://|)(?:(?:(?:blogs|download\.visualstudio|docs|msdn2?|research)\.|)microsoft|blogs\.msdn)\.co(?:m|\.\w\w)/[-_a-zA-Z0-9()=./%]*
+\b(?:https?://|)(?:(?:(?:blogs|download\.visualstudio|docs|msdn2?|research)\.|)microsoft|blogs\.msdn)\.co(?:m|\.\w\w)/[-_a-zA-Z0-9()=./%]*