feat: add 8 min buy tax

[twx-virtuals]

Note

Medium Risk
Changes bonding launch tax behavior for tokens that select the new type; impact is localized to config helpers but affects live swap tax calculation via the router.

Overview
Adds a new launch anti-sniper option ANTI_SNIPER_8M (type 5): buy-only protection for 480 seconds (8 minutes), with tax ramping from 99% down to 0% like the existing buy-side modes.

BondingConfig is updated so type 5 is accepted in isValidAntiSniperType, treated as buy-side in appliesAntiSniperOnBuy (sells unchanged), and returns 480 from getAntiSniperDuration. NatSpec for the anti-sniper helpers documents the new variant.

Callers such as FRouterV3 that already read duration and buy/sell flags from config will pick up the new type without further contract changes in this diff.

^{Reviewed by Cursor Bugbot for commit 7ad3626. Configure here.}