[mrweixd]

Description

• Fix failed SM policy creation leaving policy contexts behind when rating-group allocation fails for default, flow-rule, or traffic-influence PCC rules.
• Roll back charging data and rating groups acquired by the failed request while preserving existing sessions.
• Restore the previous policy when replacement fails, and clean up old rating groups when replacement succeeds.
• Return HTTP 500 with INSUFFICIENT_RESOURCES for rating-group allocation failures.
• Add regression tests covering allocation failures, policy replacement, and MongoDB deletion failures.

Fixes free5gc/free5gc#1202
Fixes free5gc/free5gc#1204
Fixes free5gc/free5gc#1203

Note

• Validation uses the MongoDB driver's mock responses and a local HTTP/2 UDR stub:
  • go test -race ./... passed for the implementation.
  • go test -race ./internal/sbi/processor passed after adding deletion-failure tests.
  • golangci-lint v2.11.4 passed with 0 issues.
• When MongoDB deletion fails, the error is logged and the corresponding rating group remains reserved to prevent unsafe ID reuse.
• Standards references:
  • 3GPP TS 29.512 V17.11.0, clauses 4.2.2.2, 5.3.2.3.1 and 5.7.
  • 3GPP TS 29.500 V17.11.0, clause 5.2.7.2.

[ki225]

@mrweixd LGTM. Could you please rebase this branch first? Thx