Fix parser contract errors

[tudborg]

Return parse errors instead of raising for unsupported or malformed parser paths.

• DLL unsupported control fields now return parse errors
• TPL fragmented AFL, truncated headers, and unsupported config modes return parse errors
• ELL unsupported/truncated variants and reserved session encryption modes return parse errors
• AFL truncated frames return parse errors
• Crypto wrapper error shape is consistent

Exceptions are still exceptions; no global exception swallowing.

[Copilot]

Pull request overview

This PR adjusts the parsing contract so that unsupported or malformed frames produce structured parse errors (stored in the parse context) instead of raising exceptions, improving crash resistance while keeping true exceptions as exceptions.

Changes:

• Convert several previously-raising parser paths (DLL control field variants, TPL fragmentation/header/config modes, ELL variants/session modes, AFL truncation) into {:halt, Context.add_error(...)}
• Add crash-resistance tests asserting specific error shapes for unsupported/truncated inputs
• Normalize crypto wrapper error returns to a consistent tagged tuple shape

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/crash_resistance_test.exs	Adds regression tests ensuring malformed/unsupported frames return parse errors instead of crashing.
lib/exmbus/parser/tpl/configuration_field.ex	Returns {:error, ...} for truncated/unsupported configuration field modes instead of raising/matching unsafely.
lib/exmbus/parser/tpl.ex	Converts fragmented AFL handling and TPL header parsing to return parse errors (halt with context error).
lib/exmbus/parser/ell/session_number.ex	Converts reserved ELL session encryption modes from raise to {:error, ...}.
lib/exmbus/parser/ell.ex	Uses with to propagate decode failures into parse errors; adds truncation handling for known ELL CI values.
lib/exmbus/parser/dll/wmbus.ex	Propagates unsupported control fields as parse errors and adds a safe fallback for malformed WMbus DLL frames.
lib/exmbus/parser/dll/mbus.ex	Propagates unsupported control fields as parse errors and adds a safe fallback for malformed MBus DLL frames.
lib/exmbus/parser/afl.ex	Avoids match crashes on truncated AFL by returning parse errors for truncation / non-AFL CI.
lib/exmbus/crypto.ex	Wraps crypto exceptions in a tagged error tuple for consistent downstream handling.

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