build: Upgrade to Rust 1.98 and Debian trixie

Pin the toolchain to Rust 1.98 via rust-toolchain.toml and bump the
builder image to rust:1.98-trixie. Move the runtime image from Debian
bookworm to trixie, replacing libssl3 with libssl3t64 which is the
OpenSSL runtime package name in trixie.

Dockerfile

@@ -1,5 +1,5 @@
 # Build stage
-FROM rust:1.91 AS builder
+FROM rust:1.98-trixie AS builder
 
 WORKDIR /usr/src/pop_imap_importer
 
@@ -29,11 +29,11 @@ RUN --mount=type=cache,target=/usr/local/cargo/registry \
     cargo build --release
 
 # Runtime stage
-FROM debian:bookworm-slim
+FROM debian:trixie-slim
 
 # Install CA certificates and OpenSSL runtime libraries
 RUN apt-get update && \
-    apt-get install -y ca-certificates libssl3 && \
+    apt-get install -y ca-certificates libssl3t64 && \
     rm -rf /var/lib/apt/lists/*
 
 # RUN apt-get update && apt-get install -y extra-runtime-dependencies && rm -rf /var/lib/apt/lists/*

rust-toolchain.toml

@@ -0,0 +1,2 @@
+[toolchain]
+channel = "1.98.0"