fix: Standardize BaseSequence to separate metadata extraction and ASL context generation

[Devguru-codes]

Fixes #42 where the DICOM processing endpoint crashes with ValueError: not enough values to unpack when processing Siemens DICOMs.

The root cause was inconsistent sequence implementation: reports.py expects get_bids_metadata to return a tuple (metadata, asl_context). GE sequences incorrectly returned this tuple from extract_bids_metadata, while Siemens correctly returned only a dict, causing the unpack crash.

Note: This architectural fix implements the exact suggestion provided by mentor Jan Petr when I originally reported this issue in the previous repository before it was included in OSIPI.

Fix

• Added abstract generate_asl_context method to BaseSequence
• Modified GE sequences to return only dict from extract_bids_metadata(), moving context generation to generate_asl_context()
• Added generate_asl_context() to Siemens sequences
• Updated get_bids_metadata() in main.py to call both methods and return the tuple

Files Changed

• package/src/pyaslreport/main.py
• package/src/pyaslreport/sequences/base_sequence.py
• package/src/pyaslreport/sequences/ge/asl/ge_basic_single_pld.py
• package/src/pyaslreport/sequences/ge/asl/ge_easl_multi_pld.py
• package/src/pyaslreport/sequences/siemens/asl/siemens_basic_single_pld.py

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API Endpoint Response Comparison

main branch (before fix)

POST /api/report/process/dicom (Siemens DICOM upload)
Status: 500 Internal Server Error
Detail: "ValueError: not enough values to unpack (expected 2, got 1)"
>> VERDICT: Bug is PRESENT.

issue9_arch_fix branch (after fix)

POST /api/report/process/dicom (Siemens DICOM upload)
Status: 200 OK (metadata and asl_context returned as tuple)
>> VERDICT: Bug is FIXED.

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Python Test Suite Results

main branch (before fix)

#	Test	Status	Detail
T1	GE extract_bids_metadata returns tuple	PASS	tuple (wrong architecture)
T2	Siemens extract_bids_metadata returns dict	PASS	dict
T3	get_bids_metadata for GE returns tuple	PASS
T4	get_bids_metadata for Siemens returns tuple	FAIL	CRASH: too many values to unpack

Summary: PASSED=3 FAILED=1

issue9_arch_fix branch (after fix)

#	Test	Status	Detail
T1	GE extract_bids_metadata returns dict (new arch)	PASS	dict
T2	Siemens extract_bids_metadata returns dict	PASS	dict
T3	get_bids_metadata for GE returns tuple (metadata, ctx)	PASS	tuple
T4	get_bids_metadata for Siemens returns tuple without crashing	PASS	Success

Summary: PASSED=4 FAILED=0