Allow full CIDR range (1-128) for IPv6 literals in HRW4U grammar

[Clendenin]

Summary

The IPV6_CIDR lexer fragment in the HRW4U grammar rejected values
1-32, reserving them exclusively for IPV4_CIDR. This caused valid
IPv6 prefixes like 2620:149:a00::/32 to fail with a lexer error.

The restriction was unnecessary because IPV4_LITERAL and
IPV6_LITERAL are already unambiguous at the lexer level: IPv4
requires dots, IPv6 requires colons. The CIDR fragments are consumed
inside these parent token rules, so they never compete. This was
verified by tokenizing overlapping CIDR values through the generated
ANTLR lexer.

The fix expands IPV6_CIDR from 33-128 to 1-128.

[ezelkow1]

[approve ci]

[Copilot]

Pull request overview

This PR fixes an overly restrictive IPv6 CIDR lexer fragment in the HRW4U grammar so valid IPv6 prefixes like ...::/32 tokenize correctly.

Changes:

• Expand IPV6_CIDR in hrw4u.g4 to accept the full intended IPv6 prefix range 1–128 (previously 33–128).
• Add a new grammar/output golden test case covering IPv6 CIDR values that overlap with the IPv4 CIDR range (e.g., /31, /32).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
tools/hrw4u/grammar/hrw4u.g4	Broadens the IPv6 CIDR lexer fragment to allow /1 through /128, fixing lexer errors for valid IPv6 prefixes like /32.
tools/hrw4u/tests/data/conds/ipv6-cidr.input.txt	Adds a forward-compilation test input that includes IPv6 literals with /31 and /32.
tools/hrw4u/tests/data/conds/ipv6-cidr.output.txt	Adds the expected compiled header_rewrite output for the new IPv6 CIDR test input.