feat: add p/gnoland/antisquat anti-squatting library

[politas180]

Implements p/gnoland/antisquat, a pluggable anti-squatting library for gno.land namespace management.

Closes #2727

What this PR includes

1. Working p/gnoland/antisquat package (7 files, ~500 lines + tests):

• errors.gno — Error constants
• types.gno — NameRecord, ReservedCategory, rateLimitEntry
• config.gno — Config, PricingTier, DefaultConfig()
• validation.gno — Name validation and normalization
• antisquat.gno — Main engine with 4 AVL trees, all O(log n) operations
• antisquat_test.gno — 20+ test functions

2. Design document (docs/design/antisquat-design.md)

Key design decisions (addressing @notJoon's review on #5074)

Concern	Our approach
Pricing	Correct ugnot values (1 GNOT = 1,000,000 ugnot)
Performance	O(log n) for ALL operations. No global iteration.
Pruning	Per-address pruning only. No lazy global pruning.
Protected names	Dynamic AddReservedName/RemoveReservedName via GovDAO
Auction penalties	50% deposit burn for non-revealers (configurable)
Fee handling	CalculateFee() returns fee. Package never touches coins.

Pricing tiers

Length	Annual Fee	ugnot
1-3 chars	1,000 GNOT	1,000,000,000
4 chars	100 GNOT	100,000,000
5 chars	50 GNOT	50,000,000
6-10 chars	10 GNOT	10,000,000
11+ chars	5 GNOT	5,000,000

Related: #2727, #2827, #4937

[Gno2D2]

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