feat: add MirrorNodeAccountBalanceQuery

[Dosik13]

Description:

The consensus node stops serving CryptoService/cryptoGetBalance in release 0.77, which retires
AccountBalanceQuery. Add its mirror node replacement, built to the merged
migration proposal.

• Add MirrorNodeAccountBalanceQuery, reading GET /api/v1/balances?account.id={id}
• Add MirrorNodeAccountBalance, carrying the hbar balance
• Add AccountID._MirrorNodePathID so an EVM-address alias is sent as bare hex and a public key
  alias as unpadded base32, and route the existing _MirrorNodeRequest through it
• Consolidate the mirror node REST calls onto one retry core and move FeeEstimateQuery,
  MirrorNodeContractQuery and RegisteredNodeAddressBookQuery onto it
• Add an example under examples/mirror_node_account_balance
• Fix a nil-pointer panic in PopulateAccount: it dereferenced *id.AliasEvmAddress unconditionally, so it
  panicked on any AccountID without an EVM alias.
• Skip checksum validation for IDs sent as an alias — an alias has no checksum, so
  validating one rejected the EVM-address and public-key forms SetAccountID documents
• Default the retry budget to the mirror node's 3 attempts instead of 10, capping a
  failing query at ~91s instead of ~5.7 minutes

Related issue(s):

Fixes #1792

Notes for reviewer:

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[lfdt-bot]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues

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[codecov]

Codecov Report

❌ Patch coverage is 94.94382% with 9 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
sdk/mirror_node_rest_helpers.go	93.75%	2 Missing and 2 partials ⚠️
sdk/registered_node_address_book_query.go	90.90%	1 Missing and 1 partial ⚠️
sdk/account_id.go	94.11%	1 Missing ⚠️
sdk/fee_estimate_query.go	75.00%	1 Missing ⚠️
sdk/mirror_node_contract_query.go	80.00%	0 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ
sdk/errors.go	65.51% <ø> (ø)
sdk/mirror_node.go	71.85% <100.00%> (ø)
sdk/mirror_node_account_balance_query.go	100.00% <100.00%> (ø)
sdk/account_id.go	71.95% <94.11%> (+1.12%)	⬆️
sdk/fee_estimate_query.go	82.85% <75.00%> (+4.40%)	⬆️
sdk/mirror_node_contract_query.go	68.85% <80.00%> (+1.92%)	⬆️
sdk/registered_node_address_book_query.go	87.00% <90.90%> (+7.32%)	⬆️
sdk/mirror_node_rest_helpers.go	92.55% <93.75%> (+1.92%)	⬆️

... and 2 files with indirect coverage changes

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