Fix Bot API request serialization parity gaps

[iamwavecut]

Summary

This PR fixes a set of request-serialization gaps found while comparing the library against the current Telegram Bot API request contract and behavior in other connectors.

• Serialize sendPaidMedia.media as a JSON array, as required by the Bot API, while keeping NewPaidMedia(..., *InputPaidMedia) source-compatible for single-item usage.
• Add PaidMediaConfig.MediaItems and NewPaidMediaGroup for the official 1-10 paid media item shape.
• Serialize InputSticker.sticker as the file string expected by Telegram: file_id/URL for remote files or attach://... for multipart uploads.
• Make sticker upload file collection upload-only, so FileID and URL sticker values do not overwrite the JSON InputSticker object during request preparation.
• Send required boolean false values for answerShippingQuery.ok, answerPreCheckoutQuery.ok, and editUserStarSubscription.is_canceled.
• Stop sending empty optional business_connection_id, zero reply_parameters, and zero link_preview_options objects from shared base configs.
• Make Params.AddInterface skip typed nil slices/maps/interfaces instead of serializing them as null, while preserving explicit non-nil empty slices as [].
• Add explicit opt-in flags for Bot API fields where an empty string has active semantics: sendMessageDraft, setUserEmojiStatus, setCustomEmojiStickerSetThumbnail, editForumTopic, setMyName, setMyDescription, and setMyShortDescription.

Compatibility

This is intended to be source-compatible for existing callers:

• Existing NewPaidMedia and PaidMediaConfig.Media callers continue to compile; their request payload now matches the official array shape.
• Empty-string actions are opt-in via new booleans, so accidental zero-value configs do not start clearing names, descriptions, emoji status, thumbnails, or forum icons.
• AddInterface no longer emits null for typed nil slices/maps/interfaces. Explicit empty slices still serialize as [], matching the API contract for list values.
• The only behavioral changes are request payload corrections where the previous output was missing required fields, sending non-spec shapes, or sending unintended empty optional objects.

References Checked

• Official Telegram Bot API: sendPaidMedia.media is an array of InputPaidMedia items.
• Official Telegram Bot API: InputSticker.sticker is a string accepting file_id, URL, or attach://<file_attach_name>.
• Official Telegram Bot API: selected empty strings are meaningful for draft text placeholders, emoji status removal, forum icon removal, sticker set thumbnail dropping, and bot name/description removal.
• Cross-checks against aiogram and grammY show sendPaidMedia modeled with media as a list/array and optional business parameters omitted when absent.

Verification

• go test ./...
• go vet ./...