feat: use latest SourceMod methodmaps and declarations

[Rushaway]

Closes #26

Changes

• Handle ConVar → ConVar methodmap (.IntValue, .AddChangeHook)
• OpenFile/ReadFileLine/CloseHandle → File methodmap (.ReadLine, delete)
• WritePack*/ReadPack* → DataPack methodmap
• PbReadString/BfReadString → Protobuf/BfRead methodmaps
• PbSet*/BfWrite* → Protobuf/BfWrite via UserMessageToProtobuf/UserMessageToBfWrite
• Removed the legacy CanTestFeatures()/GetFeatureStatus guard around GetUserMessageType() (always available on supported SM versions)

Fixes found along the way

• Format(TextColors[i], sizeof(TextColors), ...) used the outer array size (100) instead of the string size (256), so long color entries were truncated. Now uses strcopy(..., sizeof(TextColors[]), ...)
• Clients are stored in the timer pack as userids rather than indices, so a slot reused before the timer fires cannot get the message
• Added a null check on StartMessage
• Buffer sizes in the timer aligned to 256

Version bumped to 1.2.3.

🤖 Generated with Claude Code

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