[Bug][SubscriptionBilling]: Performance: Billing document creation does not scale to large datasets (4M+ subscription lines)

[miljance]

Introduces a suite of code-level and database-index optimizations to make billing-proposal creation, document creation, and usage-data processing scale to millions of subscription lines.

Progress & UX

• New "Progress Tracker" codeunit (8035): reusable ETA/throughput dialog, GuiAllowed-guarded, time-throttled, safe for Job Queue runs.
• Progress dialogs added to: CreateBillingDocuments, BillingProposal (create/clear/delete), GenericConnectorProcessing, ProcessUsageDataBilling.
• Recurring Billing page: cached per-row contract/partner name lookups (eliminates 10k+ uncached Gets per render); removed 9 full temp-table rebuilds from pure-navigation drilldowns; targeted group refresh for document drilldowns, Delete Billing Line, and Change Billing To Date actions.

Transaction boundaries

• BillingProposal: per-N-contract commit checkpoint (N=10) for large automated runs; test suite updated to match new commit semantics.
• CreateBillingDocuments: per-document commit checkpoint on the non-posting path.
• ProcessUsageDataBilling: removed per-commitment Commit() inside loop.

Code-level optimizations

• BillingPriceCalcSkip (new CU 8036): manual-binding subscriber that skips redundant unit-price/cost engine calls when inserting billing document lines, eliminating price-list lookups for every line.
• CreateBillingDocuments: Dictionary-based temp-billing-line aggregation replacing O(n) FindFirst per line; per-contract TrimTempBillingLines using shared-table copy to keep temp table in memory.
• BillingProposal: SetLoadFields on contract/subscription header Gets in the recursive UpdateBillingLineFromServiceCommitment path.
• FilterBillingLinesOnServiceCommitment: added Subscription Header No. filter so proposal loop seeks on existing SK1 index.
• GenericConnectorProcessing: hoisted loop-invariant GenericImportSettings Get out of the per-row loop.
• UsageBasedContrSubscribers: removed 3 event subscribers whose logic now lives directly in BillingLine.OnDelete, SalesDocuments, and PurchaseDocuments - eliminating event dispatch overhead on hot paths.
• CheckOnlyOneServicePartnerType: replaced full-scan loop with two IsEmpty() checks.

Database indexes

• BillingLine: SK7 ("Subscription Line Entry No."), TableRelation + DropDown fieldgroup added.
• BillingLineArchive: DropDown fieldgroup added.
• SubscriptionLine: Key4 ("Supplier Reference Entry No.", "Subscription Line Start Date").
• UsageDataBilling: key2-key4 reordered/extended; key5 ("Billing Line Entry No."); TableRelation for Document Type = None added so the field navigates correctly from the list.
• UsageDataGenericImport: Key2 ("Usage Data Import Entry No.", "Processing Status").

What & why

Linked work

Fixes #7690

How I validated this

• I read the full diff and it contains only changes I intended.
• I built the affected app(s) locally with no new analyzer warnings.
• I ran the change in Business Central and confirmed it behaves as expected.
• I added or updated tests for the new behavior, or explained below why none are needed.

What I tested and the outcome (required — be specific: scenarios, commands, screenshots for UI changes)

• Ran the full Subscription Billing test suite (RecurringBillingTest, UsageBasedBillingTest, contract and UBB suites); all pass.
• Verified progress dialogs (elapsed, progress, ETA, throughput) on all modified actions interactively: Create Billing Proposal, Create Documents, Clear Billing Proposal, Delete Billing Lines, Delete Documents, Process Usage Data (import and billing steps). ETA converges as expected; dialogs close cleanly on completion and do not open in headless/Job Queue sessions.
• Confirmed that drilldowns on Partner, Contract, Subscription, and Document fields in Recurring Billing refresh the affected groups without rebuilding the full proposal temp table. Opened a collective invoice document from the list, deleted it inside the card, and verified the billing lines showed cleared Document No. with correct group subtotals and no stale rows.

Risk & compatibility

• Commit boundary in CreateBillingProposal: a checkpoint is committed every 10 contracts. Any caller that holds an open page or record reference across a CreateBillingProposal call on a dataset larger than 10 contracts will see a stale-rowversion error on the next edit (BC's standard concurrency message). The two affected standard tests were updated. Third-party extensions keeping a subpage open across a proposal run would need the same treatment.
• BillingPriceCalcSkip (CU 8036): while bound during sales/purchase line initialisation, OnBeforeUpdateUnitPrice, OnBeforeGetUnitCost, OnBeforeUpdateQuantityFromUOMCode (Sales Line) and OnBeforeUpdateUnitCost (Purchase Line) are handled and skipped. A third-party subscriber using those events to apply a surcharge or override during billing document creation would be bypassed. The subscriber is bound/unbound surgically around field initialisation only; all other validation still runs.
• DeleteBillingProposal now uses per-line Delete(true) instead of DeleteAll(true): OnDelete triggers still fire identically; the only difference is that partial progress is durable on interruption. No behavioral change.
• BillingLine.OnDelete directly updates UsageDataBilling (previously via event subscriber with IsTemporary guard): AL OnDelete never fires for temporary records so the guard was redundant — no behavioral change.
• Database index additions (BillingLine SK7, UsageDataBilling key5, others) are purely additive; no data migration or upgrade codeunit needed.