goipgrep: refactor into module; pure-Go ping/resolve; cache+CI; drop binary

projects/go-tools/go/goipgrep/README.md

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+# ipgrep
+
+Extract IP addresses (and MAC addresses) from text, with optional reachability checks, reverse DNS, and ipinfo.io lookups.
+
+## Build
+
+```sh
+./scripts/build.sh
+./dist/ipgrep --help
+```
+
+## Install (local)
+
+```sh
+./scripts/build.sh
+sudo install -m 0755 ./dist/ipgrep /usr/local/bin/ipgrep
+```
+
+## Usage
+
+```sh
+# Extract IPv4 addresses from stdin
+cat file.txt | ipgrep
+
+# Extract and uniq/sort
+ipgrep -u -s file.txt
+
+# Extract MAC addresses
+ipgrep -m file.txt
+
+# Reachability filter (auto chooses ICMP if permitted, otherwise TCP probe)
+ipgrep -p file.txt
+
+# Reverse DNS (IP only)
+ipgrep -r file.txt
+
+# Lookup ipinfo.io and output CSV (default header included)
+ipgrep -l --format=csv file.txt
+```
+
+## Notes
+
+- `-p/--pingable`:
+  - `--ping-mode=auto` (default) uses ICMP echo when raw sockets are available, otherwise falls back to a TCP connect probe.
+  - ICMP echo typically requires root or `cap_net_raw` on Linux:
+    - `sudo setcap cap_net_raw+ep /path/to/ipgrep`
+- `-l/--lookup` cache:
+  - defaults to the OS cache dir (override with `--cache-path`)
+  - control size and freshness with `--cache-max-entries` and `--cache-ttl`
+- MAC `-r/--resolve` and MAC `-p/--pingable` are best-effort and rely on the local neighbor/ARP table:
+  - Linux: `/proc/net/arp`
+  - Other OSes: currently unsupported without external tooling